Russian Academy of Sciences

Landau Institute for Theoretical Physics

Previous seminars in Kapitza Institute for Physical Problems

Electron hydrodynamics in graphene: introduction and status

17 May in 11:30

D.A. Bandurin (School of Physics & Astronomy, University of Manchester, UK)

Transport in systems with many particles experiencing frequent mutual collisions (such as gases or liquids) has been studied for more than two centuries and is accurately described by the theory of hydrodynamics. It has been argued theoretically for a long time that the collective behavior of charge carriers in solids can also be treated by the hydrodynamic approach. However, despite many attempts, very little evidence of hydrodynamic electron transport has been found so far. Graphene encapsulated between hexagonal boron nitride (hBN) offers an ideal platform to study electron hydrodynamics as it hosts an ultra-clean electronic system with the electron-electron mean free path being the shortest lengths scale in the problem. In the first part of my talk we will discuss why electron hydrodynamics has not been observed before and how it manifests itself in electron transport. Furthermore, it will be shown that electrons in graphene can behave as a very viscous fluid (more viscous than honey) forming vortices of applied electron current [1]. In the second part, we will discuss the measurements of the viscosity of an electron fluid by its superballistic flow through graphene point contacts [2]. Then we will talk about the behavior of electron fluids in the presence of magnetic field where I will report the experimental measurements of the Hall viscosity in two dimensions [3]. This dissipationless transport coefficient has been widely discussed in theoretical literature on fluid mechanics, plasma physics and condensed matter physics, yet, until now, any experimental evidence has been lacking, making the phenomenon truly a unicorn. Last but not least, we will discuss how electron hydrodynamics can be used for the development of resonant terahertz photodetectors. References: [1] D.A. Bandurin, A. Principi, G.H. Auton, E. Khestanova, K.S. Novoselov, I.V Grigorieva, L.A. Ponomarenko, A.K. Geim, and M. Polini, Science 351, 1055 (2016). [2] R.K. Kumar, D.A. Bandurin, F.M.D. Pellegrino, Y. Cao, A. Principi, H. Guo, G.H. Auton, M. Ben Shalom, L.A. Ponomarenko, G. Falkovich, I.V. Grigorieva, L.S. Levitov, M. Polini, and A.K. Geim, Nat. Phys. 13, 1182 (2017). [3] A.I. Berdyugin, S.G. Xu, F.M.D. Pellegrino, R. Krishna Kumar, A. Principi, I. Torre, M. Ben Shalom, T. Taniguchi, K. Watanabe, I.V. Grigorieva, M. Polini, A.K. Geim, and D.A. Bandurin, to appear on arxiv soon. (seminar provoditsya sovmestno s laboratoriei FKS VShE)

Duality in Power-Law Localization in Disordered One-Dimensional Systems

22 March in 11:00

V.E. Kravtsov (Abdus Salam ICTP, Trieste)

The transport of excitations between pinned particles in many physical systems may be mapped to single-particle models with power-law hopping, 1/rα. For randomly spaced particles, these models present an effective peculiar disorder that leads to surprising localization properties. We show that in one-dimensional systems almost all eigenstates (except for a few states close to the ground state) are power-law localized for any value of α > 0. Moreover, we show that our model is an example of a new universality class of models with power-law hopping, characterized by a duality between systems with long-range hops (α < 1) and short-range hops (α > 1), in which the wave function amplitude falls off algebraically with the same power γ from the localization center. The paper has just been published: X. Deng, V. E. Kravtsov, G. V. Shlyapnikov, and L. Santos, Phys. Rev. Lett. 120, 110602 (2018).


Quantum simulation of Luttinger liquid physics in Josephson transmission lines

25 January in 11:30

Vladimir Manucharyan (University of Maryland)

Here we present the first quantum simulator for an impurity scattering in interacting 1D wires. The simulator consists of a transmission line made out of more than 30,000 Josephson junctions serving as a high-impedance media for microwave photons and a small phase slip Josephson junction playing the role of a back-scattering impurity. The system can be described by a boundary sine-Gordon model where the interaction strength is defined as g = Z/Rq with Z being the transmission line impedance and Rq = 6.5 kOhm the resistance quantum. By measuring scattering amplitudes and a spectrum of inelastically scattered microwave photons we can find the first and higher order correlation functions related to an AC conductance of the impurity. The controllability of the transmission line parameters and the finite size of the system allow us to fabricate lines with impedances exceeding Rq while keeping the phase slip rate of the line’s junctions very low. It gives us the unique opportunity to test Luttinger liquid physics at both sides of the critical point g = 1. A similar experimental setup can be used to simulate a Kondo impurity.

pdf, pdf

Spinovye fluktuatsii elektronov v poluprovodnikakh

16 November 2017 in 11:00

M.M. Glazov (Fiziko-tekhnicheskii institut im. A.F. Ioffe RAN)

V poslednie desyat’ let voznik interes k izucheniyu fluktuatsii spinov elektronov i elektron-dyrochnykh kompleksov v poluprovodnikakh i poluprovodnikovykh nanosistemakh. V doklade predstavlena teoriya spinovykh fluktuatsii elektronov, lokalizovannykh v poluprovodnikovykh kvantovykh tochkakh, ili svyazannykh na donorakh v ob’emnom poluprovodnike, uchityvayushchaya sverkhtonkoe vzaimodeistvie spinov nositelei zaryada so spinami yader osnovnoi reshetki. Pokazano, chto spektr spinovykh shumov neset informatsiyu kak o funktsii raspredeleniya yadernykh polei, tak i o pryzhkakh elektronov mezhdu tsentrami lokalizatsii. Analiziruyutsya proyavleniya v spektre shumov obmennogo vzaimodeistviya mezhdu elektronami, lokalizovannymi na sosednikh tsentrakh. Rezul’taty teorii sopostavleny s dannymi eksperimentov. Literatura: [1] M. M. Glazov and E. L. Ivchenko, Spin noise in quantum dot ensembles, Phys. Rev. B 86, 115308 (2012). [2] D.S. Smirnov, M.M. Glazov, E.L. Ivchenko, Vliyanie obmennogo vzaimodeistviya na spinovye fluktuatsii lokalizovannykh elektronov, FTT 54, 254 (2014). [3] M. M. Glazov, Spin noise of localized electrons: Interplay of hopping and hyperfine interaction, Phys. Rev. B 91, 195301 (2015). [4] A. V. Shumilin, E. Ya. Sherman, and M. M. Glazov, Spin dynamics of hopping electrons in quantum wires: Algebraic decay and noise, Phys. Rev. B 94, 125305 (2016). [5] Ph. Glasenapp, D. S. Smirnov, A. Greilich, J. Hackmann, M. M. Glazov, F. B. Anders, and M. Bayer, Spin noise of electrons and holes in (In,Ga)As quantum dots: Experiment and theory, Phys. Rev. B 93, 205429 (2016).

Interaction induced topological phases in one dimension

14 September 2017 in 11:30

Sam Carr (University of Kent, England)

We consider a one-dimensional single channel quantum wire with a spin gap but gapless charge excitations. We show that the spin gap can be generated in two different ways, one of which has non-trivial topological properties. This topology manifests itself in two ways - firstly in the existence of gapless single-particle edge states, and secondly in an insensitivity of the wire to weak impurities reminiscent of the helical edge states of two dimensional topological insulators. We will demonstrate a number of ways such a phase of matter can be engineered, including spin-orbit quantum wires or two coupled helical edge states. If time permits, we will also touch on recent work concerning strong impurities in such systems. References: [1] Kairanis and Carr, PRB 92, 035139 (2015). [2] Santos, Gutman and Carr, PRB 93, 235436 (2016). [3] Kainaris, Santos, Gutman and Carr, Forschr. Phys. 1600054 (2017). [4] Kainaris, Carr and Mirlin, coming soon.

Vliyanie elektron-elektronnogo rasseyaniya na provodimost’ mnogomodovykh ballisticheskikh kontaktov i kanalov

25 May 2017 in 11:30

K.E. Nagaev (IRE, teoriya), V.S. Khrapai (IFTT, eksperiment)

Privodyatsya teoreticheskie i eksperimental’nye rezul’taty po elektroprovodnosti shirokikh ballisticheskikh kontaktov v dvumernom elektronnom gaze pri nalichii elektron-elektronnogo rasseyaniya za predelami gidrodinamicheskogo priblizheniya. Obsuzhdayutsya lineinaya zavisimost’ popravki k elektroprovodnosti ot temperatury i polozhitel’noe magnetosoprotivlenie v slabykh polyakh. Rassmatrivaetsya takzhe protivopolozhnyi sluchai dlinnogo kanala s gladkimi stenkami.

Together we can: transport properties of electron viscous flows

27 April 2017 in 11:30

L. Levitov (MIT)

Strongly interacting electrons can move in a neatly coordinated way, reminiscent of the movement of viscous fluids. In viscous electron flows interactions give rise to a collective behavior, facilitating transport and allowing conductance to exceed the fundamental Sharvin-Landauer ballistic limit Gball. This talk will describe a theory of the ballistic-to-viscous crossover in a constriction exhibiting the ballistic transport at T = 0 but governed by electron hydrodynamics at elevated temperatures. An approach based on quasi-hydrodynamic variables predicts an additive relation G = Gball + Gvis, where the viscous contribution Gvis dominates over Gball in the hydrodynamic limit. We will also discuss recent measurements of electron transport through graphene constrictions, finding that conductance below 150 K increases with increasing temperature. The measurements help to identify the conductance contribution arising due to electron viscosity and determine its temperature dependence. Besides fundamental interest, this work shows that viscous effects can facilitate high-mobility transport at elevated temperatures, a potentially useful behavior for designing graphene-based devices.

Indutsirovannaya magnitnym polem prozrachnost’ kvantovogo metamateriala, sostoyashchego iz zerkal’nykh potokovykh kubitov

12 January 2017 in 11:30

Kirill Shulga (Russian Quantum Center and MISiS)

V svoem doklade ya rasskazhu ob obnaruzhennom nami effekte, voznikayushchem v kvantovom sverkhprovodyashchem metamateriale v predele sil’noi svyazi. Metamaterial sostoit iz tsepochki meta-atomov (kubitov), kazhdyi iz kotorykh soderzhit dva sverkhprovodyashchikh kol’tsa, soedinennykh tunnel’nym perekhodom. Elektromagnitnye svoistva takogo materiala mogut byt’ opisany kvantovoi induktivnost’yu kazhdogo atoma, kotoroi mozhno upravlyat’ v shirokom chastotnom diapazone pri pomoshchi izmeneniya vneshnego magnitnogo polya. Rezkoe podavlenie prokhozhdeniya mikrovolnovogo izlucheniya cherez takoi metamaterial chereduetsya s ego rezonansnym usileniem, voznikayushchim iz-za rasshchepleniya mezhdu vyrozhdennymi potokovymi sostoyaniyami. Osnovnoe sostoyanie sistemy mozhet byt’ pereklyucheno v sostoyanie superpozitsii dvukh potokovykh sostoyanii, prilozheniem k obraztsu magnitnogo polya opredelennoi velichiny. Budet predstavleno neskol’ko kvantovykh modelei povedeniya takoi sistemy, kotorye mogut opisat’ poluchennye eksperimental’nye dannye.

Replica approach with one step replica symmetry breaking in the problem of Anderson localization on the Bethe lattice

29 December 2016 in 11:30

V.E. Kravtsov (Abdus Salam ICTP, Trieste)

We formulate general criteria for localized, extended ergodic and extended non-ergodic (multifractal) phases in disordered quantum systems and apply these criteria to the problem of Anderson localization on Bethe lattice, random regular graphs and generalized Rosenzweig-Porter random matrix ensemble. We focus on the replica symmetry breaking approach to the problem and show how this approach provides a natural classification of phases and phase transitions.

Finite-temperature conductance of strongly interacting quantum wire with a helical nuclear spin order

15 December 2016 in 11:30

Pavel Aseev (University of Basel)

We study the temperature dependence of the electrical conductance of a clean strongly interacting quantum wire in the presence of a helical nuclear spin order. The nuclear spin helix opens a temperature-dependent partial gap in the electron spectrum. Using a bosonization framework we describe the gapped electron modes by sine-Gordon-like kinks. We predict an internal resistivity caused by an Ohmic-like friction these kinks experience via interacting with gapless excitations. As a result, the conductance rises from G=e^2/h at temperatures below the critical temperature when nuclear spins are fully polarized to G=2e^2/h at higher temperatures when the order is destroyed, featuring a relatively wide plateau in the intermediate regime. The theoretical results are compared with the experimental data for GaAs quantum wires obtained recently by Scheller et al. [Phys. Rev. Lett. 112, 066801 (2014)]. (arXiv:1611.10238)

O podschete chisla tochek ravnovesiya v neuporyadochennykh sistemakh

8 December 2016 in 11:30

Yan Fyodorov (King's College London)

Ya planiruyu obsudit’ kratko dve raboty, svyazannye obshchei ideologiei o podschete chisla tochek ravnovesiya v neuporyadochennykh sistemakh. V pervoi chasti, sleduya rabote ArXiv:1610.04831, ya opishu, kak takaya zadacha reshaetsya dlya nerelaksatsionnoi dinamiki v modeli tipa spinovogo stekla na sfere bol’shoi razmernosti, i obsuzhu fazovyi perekhod v rezhim eksponentsial’no bol’shogo chisla tochek ravnovesiya. Vo vtoroi chasti (osnovannoi na eshche ne zavershennoi rabote s P. Le Doussal i C. Texier) ya kratko obrisuyu podschet chisla tochek ravnovesiya dlya napravlennogo polimera v sluchainom potentsiale, gde zadacha svoditsya k izucheniyu fluktuatsii pokazatelya Lyapunova v odnomernoi lokalizatsii v rezhime lifshitsevskogo khvosta.

Experimental search for one-dimensional edge states at surface steps of the topological insulator Bi2Se3

1 December 2016 in 11:30

S.V. Zaitsev-Zotov (Kotel’nikov IRE RAS, Moscow)

Results of detailed study of the topological insulator Bi2Se3 surface state energy structure in the vicinity of surface steps by scanning tunneling microscopy (STM) and spectroscopy (STS) methods are described. Increase of the chemical potential in the vicinity of the step edge is observed. The value of the increase is found to correlate with the step height and is caused by redistribution of electron wave functions between outer and inner edges of surface steps, as it is known for usual metals, as well as by presence of dangling bonds on the step. Smaller value of the shift and its larger characteristic length reflect specifics of the helical surface states. This increase is accompanied by enhancement of the relative value of the differential tunneling conductance, dI/dV, at the Dirac point and thereby produces an illusion of appearance of edge states. We show that the enhancement is reproduced in the framework of the tunneling model, which takes into account the dependence of the tunneling gap transparency on the voltage. References: [1] N.I. Fedotov, S.V. Zaitsev-Zotov, JETP Letters, 104, #11 (2016) (in press); arXiv:1609.08294. [2] N.I. Fedotov, S.V. Zaitsev-Zotov, arXiv:1609.08911.

Elementarnye poverkhnostnye khimicheskie reaktsii. Kak i dlya chego ikh ispol’zovat’

3 November 2016 in 11:30

K.N. El’tsov (IOF im. A.M. Prokhorova RAN, Moskva)

Soderzhanie: 1. Kak izuchayut khimicheskie i strukturnye prevrashcheniya poverkhnosti pri vozdeistvii aktivnykh gazov; 2. Vzaimodeistvie molekulyarnykh galogenov s poverkhnost’yu metallov; 3. Nachal’nye stadii okisleniya metallov; 4. Rost grafena na poverkhnosti Ni(111); 5. Elektronno-stimulirovannye protsessy v zone deistviya igly STM; 6. Razrabotka operatsii atomnogo masshtaba na poverkhnosti dlya sozdaniya elementov kvantovogo komp’yutera. V doklade budut predstavleny rezul’taty, poluchennye s ispol’zovaniem sverkhvysokovakuumnoi skaniruyushchei tunnel’noi mikroskopii (STM), dlya sistem «aktivnyigaz/poverkhnost’» v shirokom diapazone stepenei pokrytiya adsorbatom. Budet pokazano, chto elementarnyi khimicheskii protsess tipa Cl+Cu=CuCl s predstavlyaet soboi kompleks dvumernykh fazovykh perekhodov, vklyuchayushchii formirovanie odnomernykh atomnykh tsepochek, formirovanie i szhatie dvumernykh reshetok, kondensatsiyu kraudionov, rekonstruktsiyu i obrazovanie novogo dvumernogo i/ili ob’emnogo kristallov. Budut rassmotreny elektronno-stimulirovannye poverkhnostnye khimicheskie reaktsii v zone deistviya igly STM, chto pozvolyaet ispol’zovat’ ikh dlya lokal’nykh vozdeistvii na atomnom urovne.

Drozhanie elektronov i spin-gal’vanicheskii effekt v poluprovodnikakh

13 October 2016 in 11:30

S.A. Tarasenko (FTI im. A.F. Ioffe RAN, Sankt-Peterburg)

Pokazano, chto elektrony provodimosti v poluprovodnikovykh strukturakh so spin-orbital’nym vzaimodeistviem vo vneshnem magnitnom pole ispytyvayut drozhanie. Drozhashchee dvizhenie (Zitterbewegung) voznikaet v otsutstvie peremennoi sily, ego priroda analogichna prirode Zitterbewegung svobodnykh dirakovskikh elektronov. V doklade obsuzhdayutsya rezul’taty pervogo eksperimental’nogo i teoreticheskogo issledovaniya kogerentnogo drozhaniya elektronov, indutsirovannogo opticheskoi orientatsiei ansamblya elektronov v odinakovoe spinovoe sostoyanie.

Dissipation-induced topological insulators: A recipe

22 September 2016 in 11:30

Moshe Goldstein (Tel-Aviv University)

It has recently been realized that driven-dissipative dynamics, which usually tends to destroy subtle quantum interference and correlation effects, could actually be used as a resource. By proper engineering of the reservoirs and their couplings, one may drive a system towards a desired quantum-correlated steady state, even in the absence of internal Hamiltonian dynamics. An intriguing class of quantum phases is characterized by topology, including the quantum Hall effect and topological insulators and superconductors. Which of these noninteracting topological states can be achieved as the result of purely dissipative Lindblad-type dynamics? Recent studies have only provided partial answers to this question. In this talk, I will present a general recipe for the creation, classification, and detection of states of the integer quantum Hall and 2D topological insulator type as the outcomes of coupling a system to reservoirs, and show how the recipe can be realized with ultracold atoms and other quantum simulators. The mixed states so created can be made arbitrarily close to pure states, and the construction may be generalized to other topological phases.

Spiraling energy dispersion of arc states in Weyl semimetals

15 September 2016 in 11:30

Anton Andreev (University of Washington, Seattle,USA)

Weyl semimetals are recently discovered materials in which the valence and conduction bands touch at isolated points (Weyl nodes) in the Brillouin zone. This gives rise to unusual electronic properties of these materials. In particular, Weyl semimetals host peculiar surface electron states whose Fermi lines are shaped as open arcs. I will show that static electric fields that are necessarily present near the crystal surface result in a spiraling structure of Fermi arcs. The winding angle of the spiral is controlled by the chirality of the Weyl node and the magnitude of the surface potential. I will also discuss magnetoresistance of a pn-junction in a Weyl semimetal.

Random matrix approach to the jamming transition

9 June 2016 in 11:30

Ya.M. Bel’tyukov (FTI im. A.F. Ioffe RAN, Sankt-Peterburg)

Amorphous materials as diverse as foams, emulsions, colloidal suspensions and granular media can jam into a solid-like disordered state. In this state each particle has a certain equilibrium position and can vibrate around it. In this talk, I will show that the dynamical matrix M describing harmonic oscillations in such media can be represented in the form M = AAT. The rows of the matrix A correspond to the degrees of freedom of individual granules and its columns correspond to elastic contacts between granules. This representation allows to apply the random matrix theory and estimate the vibrational density of states. The resulting vibrational density of states is approximately constant over a wide frequency range which is determined mostly by the ratio of the number of degrees of freedom and the total number of elastic contacts in the system. The results are in a good agreement with numerical experiments performed by various authors.

Majorana fermion from Landau quantization in 2D topological superconductors

2 June 2016 in 11:30

A.V. Rozhkov (MFTI; ITPE RAN; VNIIA im. Dukhova)

We study the generation of Majorana fermions in a two-dimensional topological superconductor placed in a transverse magnetic field B. A topological insulator/superconductor heterostructure and a two-dimensional p-wave superconductor are discussed. It is demonstrated that in these systems a single vortex creates two Majorana fermions, one hosted at the vortex core. The wave function of the second Majorana state is localized in the superconductor volume along a circle of radius rB−1 centered at the vortex core. In the case of many vortices, the sensitivity of r to the magnetic field B may be used to control the coupling between the Majorana fermions. The latter property could be an asset for quantum computations.

Dolgovremennye fluktuatsii izlucheniya nanorazmernykh chastits

12 May 2016 in 11:30

Pavel Frantsuzov (Novosibirsk)

Odinochnye nanorazmernye chastitsy, takie kak kolloidnye poluprovodnikovye nanokristally, nanosterzhni (nanorods), nanoprovoloki (nanowires) demonstriruyut fluktuatsii intensivnosti fluorestsentsii (mertsanie) na shirochaishem spektre vremennykh masshtabov, ot dolei millisekund do chasov. V doklade budut obsuzhdat’sya sushchestvuyushchie teoreticheskie mekhanizmy i modeli mertsaniya nanochastits, vklyuchaya model’ Efrosa/Rozena [Al.L. Efros & M. Rosen, Phys. Rev. Lett. 78, 1110 (1997)] i Multiple recombination center model [P.A. Frantsuzov, S. Volkan-Kacso & B. Janko, Phys. Rev. Lett. 103, 207402 (2009)].

Electro-Convective Instability in Concentration Polarization

28 April 2016 in 11:30

Boris Zaltzman (Blaustein Institutes for the Desert Research, Ben-Gurion University of the Negev)

DC ionic current in a binary electrolyte passing through a perm-selective interface (electrode, ion exchange membrane, micro-nano-channel junction) is a basic element of many electrochemical engineering and micro-fluidic processes, such as electrodeposition, electrodialysis and protein pre-concentration. Such current passage is diffusion-limited in the sense that it induces a decrease of electrolyte concentration towards the interface, known as concentration polarization (CP), whose expression is the saturation of current upon increasing voltage at some value known as the limiting current. Upon a further increase of voltage, this saturation is followed by a relatively rapid current increase — the so-called over-limiting conductance (OLC) regime. The mechanism of OLC remained unexplained for a long time. Only recently was it shown that in open systems OLC is due to the destruction of the diffusion layer by a micro-scale vortical flow which spontaneously develops as a result of Electro-Convective Instability near the limiting current and provides an additional ionic transport mechanism. This instability has attracted interest of both theoreticians and experimentalists. Commonly, it has been attributed to non-equilibrium electro-osmosis (EO) related to the extended space charge (ESC), which develops at the limiting current. One reason for this attribution was the realization that for a perfectly perm-selective solid, neither equilibrium EO nor bulk electric force can yield Electro-Convective Instability. On the other hand, it has been shown that non-equilibrium EO can. In the early studies, perfect perm-selectivity was assumed for the sake of simplicity. The subsequent studies of various time-dependent and nonlinear features of EO instability continued to make this assumption, while recognizing that the ESC is essentially identical for a perfect and non-perfect interface. Recently, we reported that relaxing the assumption of perfect perm-selectivity allows for equilibrium Electro-Convective Instability, irrespectively of any ESC effects. Generally, electro-convection is driven by the electric force acting both upon the space charge of an interfacial electric double layer (EDL) and the residual space charge of the quasi-electroneutral bulk. A slip-like flow induced by the former is EO, whereas the flow induced by the latter is bulk electroconvection. There are two regimes of EO that correspond to different states of the EDL and are controlled by the non-equilibrium voltage drop across it: equilibrium EO and non-equilibrium EO. While both regimes result from the action of a tangential electric field upon the space charge of the EDL, the former relates to the charge of the equilibrium EDL, whereas the latter relates to the ESC of the non-equilibrium EDL. For a perfectly perm-selective interface CP under the equilibrium EO slip condition is stable. So it is for bulk electro-convection in a low molecular electrolyte. As was recently shown, imperfect perm-selectivity makes equilibrium instability possible, driven by either equilibrium EO or bulk electro-convection, or both. Thus, depending on perm-selectivity, the Electro-Convective Instability in CP may be either driven or inhibited by several factors, such as equilibrium or non-equilibrium EO, bulk electroconvection, diffusio-osmosis, etc. The first results on identifying and analyzing the interplay of these major ’surface’ and ’bulk’ factors for varying perm-selectivity of the interface will be presented.

Protsessy perevorota spina i radiatsionnoe zatukhanie tyomnykh eksitonov v dikhalkogenidakh perekhodnykh metallov

21 April 2016 in 11:30

D. Basko (LPMMC, CNRS, Grenoble, France)

Dvumernye monosloi soedinenii MoS2, MoSe2, WS2, WSe2 yavlyayutsya pryamoshchelevymi poluprovodnikami s opticheskoi (eksitonnoi) shchel’yu v vidimom diapazone. Shchel’ nakhoditsya v dvukh elektronnykh dolinakh, svyazannykh simmetriei obrashcheniya vremeni. Iz-za sil’nogo spin-orbital’nogo vzaimodeistviya zony rasshchepleny po spinu. Znaki rasshchepleniya v raznykh dolinakh protivopolozhny. Iz 16 vozmozhnykh eksitonnykh sostoyanii s raznymi kombinatsiyami spinovykh i dolinnykh indeksov elektrona i dyrki, tol’ko 4 mogut annigilirovat’ bez perevorota spina i/ili doliny. Ostal’nye sostoyaniya nazyvayutsya tyomnymi. V dannoi rabote rassmatrivayutsya tyomnye eksitony, raspad kotorykh razreshyon po doline, no zapreshchyon po spinu.

Electronic phase transitions induced by electric or optical impacts

4 February 2016 in 11:30

Serguei Brazovskii

Controlled transformations of electronic states or even of whole phases are achievable today by impacts of very strong electric fields and/or the ultrafast optical pumping. The experimental success is coming from ferroelectrically and ionically enhanced field effect in high-Tc superconductors, induced metallization in oxides of transition metals and in organic materials, field-effect superconductivity in MBE monolayers. The techniques of the femto-second optical pumping span from the purely optical setups to the newer time-resolved photoemission spectroscopy and to the latest time-sliced diffraction. The tested electronic phases include: superconductivity, charge density waves, charge ordering, ferroelectricity, magnetic phases, Peierls and Mott insulators. A super goal is to attend “hidden” states which are inaccessible and even unknown under equilibrium conditions. Such a bistable switching has been achieved in a “polaronic Wigner-crystalline Mott insulator” 1T-TaS2. After the experimental review, some time will be devoted to a phenomenological theory (collaboration with N. Kirova). Thus, the modeling of the quasi-condensate of excitons interacting with the order parameter recovers the dynamical realization of the “excitonic insulator” state and spacio-temporal patterns with self-focusing, domains segregation, and local dynamical phase transitions.

Poperechnaya migratsiya malykh sfericheskikh chastits v sdvigovykh i nestatsionarnykh potokakh

21 January 2016 in 11:30

E.S. Asmolov (TsAGI, NII Mekhaniki MGU, IFKhE im. A.N.Frumkina RAN)

V rabote na osnove metodov vozmushchenii i srashchivaemykh asimptoticheskikh razlozhenii sformulirovana zadacha o dinamike sfericheskikh chastits v sdvigovykh i nestatsionarnykh potokakh pri malykh, no konechnykh chislakh Reinol’dsa. Techenie vo vnutrennei oblasti (na masshtabe radiusa chastitsy) v glavnom priblizhenii po chislu Reinol’dsa sootvetstvuet klassicheskoi zadache Stoksa ob obtekanii sfery odnorodnym neogranichennym potokom. Raspredelenie skorosti vo vneshnei oblasti (na masshtabe Sefmana) opisyvaetsya uravneniyami Ozeena. Rasschitany inertsionnye poperechnye sily, deistvuyushchie na chastitsy, v sdvigovykh (lineinyi potok i techenie v kanale) potokakh dlya razlichnykh napravlenii i velichin skorosti skol’zheniya, opredeleny ustoichivye polozheniya ravnovesiya chastits. Postroeno asimptoticheskoe reshenie dlya vozmushchennogo polya skorosti vdali ot ne neitral’no plavuchei chastitsy v sdvigovom potoke. Polucheny stepennye zakony zavisimostei vozmushchenii vsekh komponent skorosti ot rasstoyaniya do chastitsy v dal’nei nevyazkoi oblasti i v vyazkikh sledakh. Resheny zadachi o techeniyakh gazovzvesi pod deistviem poperechnoi sily v laminarnykh pogranichnykh sloyakh na razlichnykh telakh.

Recent identifications of microscopic solitons in quasi 1D electronic systems and generalisations to higher dimensions

10 December 2015 in 11:30

Serguei Brazovskii

We review a progress in experiments and theory, elucidating the role of microscopic solitons in quasi-1D electronic systems with a symmetry breaking. The new interest rises from studies of the «electronic ferroelectricity» in organic conductors, and from nano-scale tunneling experiments in Charge Density Wave (CDW) materials. Individual solitons have been visually captured in recent STM experiments. On this basis we extrapolate to a picture of combined topological excitations in general strongly correlated systems: from doped antiferromagnets to strong coupling and spin-polarized superconductors. At more macroscopic scales, we recover the electronic vortices generated in mesa-junctions, and domain walls evolving in femtosecond pump-probe experiments.

Elektrodinamika sloistykh gibridnykh struktur sverkhprovodnik/ferromagnetik/sverkhprovodnik v okrestnosti 0-π perekhoda

26 November 2015 in 11:30

A.V. Samokhvalov (IFM RAN, Nizhnii Novgorod)

Gibridnye struktury sverkhprovodnik/ferromagnetik/sverkhprovodnik (SFS) s effektom blizosti yavlyayutsya udobnym ob’ektom dlya izucheniya fazovykh perekhodov, vyzvannykh vzaimodeistviem dvukh konkuriruyushchikh parametrov poryadka: sverkhprovodyashchego i ferromagnitnogo. Neobychnoe povedenie sloistykh SF struktur, kak pravilo, svyazano s interesnym yavleniem π-sverkhprovodimosti pri kotorom v gibridnoi strukture formiruetsya ravnovesnoe sostoyanie s netrivial’noi raznost’yu faz π mezhdu sosednimi sverkhprovodnikami. Effekt blizosti na SF granitsakh privodit k chastichnomu ili polnomu podavleniyu sverkhprovodimosti v S sloyakh, a velichina effekta zavisit ot struktury parnoi volnovoi funktsii, t.e. ot tipa sostoyaniya (0 ili π), kotoroe ustanavlivaetsya v SFS strukture. V doklade obsuzhdayutsya prichiny rezkogo uvelicheniya effektivnoi glubiny proniknoveniya magnitnogo polya λ(T) pri ponizhenii temperatury T, kotoroe nablyudalos’ v diffuznykh SFS strukturakh Nb/PdNi/Nb s tonkimi (poryadka sverkhprovodyashchei dliny kogerentnosti) S sloyami [1]. Predlozhena model’, ob’yasnyayushchaya podobnuyu anomaliyu proyavleniem fazovogo perekhoda mezhdu 0 i π sverkhprovodyashchimi sostoyaniyami SFS struktury. Osnovyvayas’ na mikroskopicheskikh uravneniyakh Uzadelya, polucheno razlozhenie Ginzburga—Landau, koeffitsienty kotorogo zavisyat ot raspredeleniya parnoi volnovoi funktsii v ferromagnetike i razlichny dlya 0 i π sostoyanii SFS struktury. Vypolneny raschety svobodnoi energii 0 i π sostoyanii, temperatury 0−π perekhoda, i privedena fazovaya diagramma SFS struktury na ploskosti parametrov (temperatura — tolshchina F sloya). Perekhod mezhdu 0 i π sostoyaniyami pri izmenenii temperatury proiskhodit po tipu fazovogo perekhoda pervogo roda, soprovozhdaetsya skachkoobraznym izmeneniem amplitudy volnovoi funktsii v S sloyakh i, kak sledstvie, rezkim izmeneniem ekraniruyushchikh svoistv SFS struktury. Priveden obobshchennyi funktsional Ginzburga—Landau, spravedlivyi dlya proizvol’noi raznosti faz sverkhprovodyashchikh parametrov poryadka S sloev, i vypolneny raschety tok-fazovoi zavisimosti SFS dzhozefsonovskogo perekhoda s tonkimi sverkhprovodyashchimi elektrodami v okrestnosti perekhoda mezhdu 0 i π sostoyaniyami [2]. Literatura: [1] N. Pompeo et al., Phys. Rev. B 90, 064510 (2014). [2] A. V. Samokhvalov and A. I. Buzdin, Phys. Rev. B 92, 054511 (2015).

Thermal transport in the disordered electron liquid

12 November 2015 in 11:30

Georg Schwiete (SPICE and Johannes Gutenberg Universität Mainz, Germany)

In this talk, I will present a theoretical study of thermal transport in the disordered two-dimensional electron liquid. At temperatures smaller than the impurity scattering rate, in the diffusive regime, thermal conductivity acquires non-analytic quantum corrections. Our approach to this problem is based on an analysis of the heat density-heat density correlation function. To this end, Luttinger’s gravitational potentials are introduced in the action as sources that couple to the heat density. In a two-stage procedure, a renormalization group calculation based on the Keldysh non-linear sigma model in the presence of Luttinger’s gravitational potentials is supplemented with a perturbative study of scattering processes induced by the Coulomb interaction in the sub-temperature energy range. These scattering processes are at the origin of logarithmic corrections violating the Wiedemann-Franz law. As an application, I intend to discuss thermal transport on the metallic side of the metal-insulator transition in Si MOSFETs. References: G. Schwiete and A.M. Finkel’stein, PRB 90, 060201 (2014); PRB 90, 155441 (2014); arXiv:1509.02519; arXiv:1510.06529.

The Essentially Entangled Component of Multipartite Mixed Quantum States, its Properties and an Efficient Algorithm for its Extraction

22 October 2015 in 11:30

V.M. Akulin, G.M. Kabatyanski, A.Mandilara

We introduce a density matrix decomposition of a multipartite quantum system of a finite dimension into two density matrices: a separable one and an essentially entangled one, which contains no product states components. This convex decomposition can be achieved in practice with the help of an algorithm based on linear programming, which in the general case scales polynomially with the dimension of the system. We prove that the rank of the essentially entangled component is always lower than that of the initial density matrix and we give an upper bound for this rank. We illustrate the algorithm at an example of a composed system of total dimension 12 undergoing loss of coherence due to classical noise and we trace the time evolution of its essentially entangled component. We suggest a geometric description of entanglement dynamics and show how it explains the well-known phenomena of sudden death and revival of multipartite entanglement. Interestingly, while we observe a weight loss of the essentially entangled component with time, its average entanglement content is not affected by the coherence loss.

Dynamical Lamb effect in a tunable superconducting qubit-cavity system

10 September 2015 in 11:30

D.S. Shapiro (Vserossiiskii NII avtomatiki im. N.L. Dukhova; IRE im. V.A. Kotel’nikova RAN), A.A. Zhukov, V.V. Pogosov, Yu.E. Lozovik

Dinamicheskii effekt Lemba yavlyaetsya odnim iz vozmozhnykh mekhanizmov parametricheskogo vozbuzhdeniya atoma v rezonatore [A.M. Fedotov, N.B. Narozhny, and Yu.E. Lozovik, PRA 64, 053807 (2001)]. Effekt voznikaet v rezul’tate modulyatsii lembovskogo sdviga atoma za schet, naprimer, neadiabaticheskogo izmeneniya chastoty fotonnoi mody. Tem ne menee, v sisteme s perestraivaemym rezonatorom etot mekhanizm vozbuzhdeniya slozhno izolirovat’ ot drugikh kanalov, svyazannykh s generatsiei i pogloshcheniem kazimirovskikh fotonov. V doklade predlozhena al’ternativnaya realizatsiya dinamicheskogo effekta Lemba, kotoraya vozmozhna v sovremennykh sverkhprovodnikovykh sistemakh kubit-rezonator v rezhime perestraivaemoi energii svyazi. Pokazano, chto imenno za schet neadiabaticheskogo pereklyucheniya energii vzaimodeistviya mozhno modulirovat’ lembovskii sdvig i vozbuzhdat’ kubit v otsutstvie fotonnoi nakachki. Takoi podkhod pozvolyaet izbezhat’ rozhdeniya kazimirovskikh fotonov, chto yavlyaetsya klyuchevym obstoyatel’stvom dlya realizatsii dinamicheskogo effekta Lemba. Dinamika sistemy opisyvaetsya v ramkakh nestatsionarnoi modeli Rabi dlya edinichnogo i periodicheskogo pereklyuchenii energii svyazi kubita i rezonatora. [D.S. Shapiro, A.A. Zhukov, W.V. Pogosov, Yu.E. Lozovik, "Dynamical Lamb effect in a tunable superconducting qubit-cavity system", Phys. Rev. A 91, 063814 (2015); arXiv:1503.01666]

Interferentsiya fononov v atomarnykh metazerkalakh, «fononnykh kondensatorakh» i v teploperenose cherez granitsy razdela kristallov

21 May 2015 in 11:30

Yu.A. Kosevich (Institut khimicheskoj fiziki im. N.N. Semenova RAN)

Seminar budet posvyashchen opisaniyu novykh nizkorazmernykh metamaterialov i transportnykh yavlenii, v kotorykh vazhnuyu rol’ igraet interferentsiya fononov na atomarnykh defektakh reshetki kristalla. Budet pokazano, chto vozmozhno rezonansnoe polnoe otrazhenie ili polnoe pogloshchenie fonona dvumernym defektom reshetki, effektivnaya tolshchina kotorogo znachitel’no men’she dliny volny fonona. Chastoty takikh rezonansov opredelyayutsya dinamicheskimi svoistvami defektnoi ploskosti. Yavlenie polnogo otrazheniya (antirezonansa prokhozhdeniya) vozmozhno, v chastnosti, na monoatomnoi kristallicheskoi ploskosti, chastichno zapolnennoi atomarnymi defektami, i na dvumernom defekte reshetki, v kotorom sushchestvenny vzaimodeistviya kak blizhaishikh, tak i ne blizhaishikh sosedei. Analiz etikh yavlenii pokazyvaet, chto opredelyayushchuyu rol’ v nikh, v otlichie ot rezonansa Fano, igraet destruktivnaya interferentsiya fononov, rasprostranyayushchikhsya cherez dvumernyi defekt po dvum putyam: po silovym svyazyam atomov matritsy i defektov, ili po svyazyam blizhaishikh i ne blizhaishikh sosedei. Pokazano, chto sluchainoe raspredelenie defektov v kristallicheskoi ploskosti i angarmonizm silovykh svyazei ne razrushayut interferentsionnyi antirezonans. Shirinu antirezonansnogo pika otrazheniya mozhno svyazat’ s dlinoi kogerentnosti fononnogo volnovogo paketa, kak i v sluchae destruktivnoi interferentsii fotonnykh volnovykh paketov v effekte Khonga-U-Mandela. Pokazano, chto destruktivnaya interferentsiya fononov ponizhaet teplovoi kondaktans granitsy razdela kristallov, chastichno zapolnennoi rezonansnymi atomarnymi defektami. Na osnove atomarnykh metazerkal mozhet byt’ postroen ul’tra kompaktnyi «fononnyi kondensator» dlya khraneniya i izlucheniya kogerentnykh teragertsovykh fononov. Vse osnovnye predstavlennye vyvody podtverzhdayutsya analiticheskimi raschetami ekvivalentnykh kvaziodnomernykh reshetok i molekulyarno-dinamicheskim modelirovaniem realistichnykh trekhmernykh reshetok. [Literatura: 1. Yu.A. Kosevich «Capillary phenomena and macroscopic dynamics of complex two-dimensional defects in crystals», Progr. Surf. Sci. 55, 1 (1997). 2. Yu.A. Kosevich «Mnogokanal’noe rasprostranenie i rasseyanie fononov i fotonov v nizkorazmernykh nanostrukturakh», UFN 178(8), 884 (2008). 3. H. Han, L. Potyomina, A.A. Darinskii, S. Volz, and Yu.A. Kosevich «Phonon interference and thermal conductance reduction in atomic-scale metamaterials», Phys. Rev. B 89(R), 180301 (2014). 4. H. Han, B. Li, S. Volz, and Yu.A. Kosevich «Ultracompact interference phonon nanocapacitor for storage and lasing of coherent terahertz lattice waves», Phys. Rev. Lett. 114, 145501 (2015).]

O roli effekta Landau-Zinera v rabote kvantovogo turniketa

7 May 2015 in 11:30

D. Basko (LPMMC, CNRS, Grenoble, France)

Kvantovyi turniket predstavlyaet soboi nanoelektronnoe ustroistvo, kontroliruemym obrazom perenosyashchee elektrony po odnomu mezhdu dvumya sverkhprovodyashchimi elektrodami putyom podachi peremennogo napryazheniya na metallicheskuyu nanochastitsu, raspolozhennuyu mezhdu dvumya elektrodami. Okazyvaetsya, chto kogerentnaya svyaz’ mezhdu elektronnymi sostoyaniyami v nanochastitse i kvazichastichnymi sostoyaniyami v sverkhprovodnikakh nakladyvaet fundamental’nye ogranicheniya na rabotu ustroistva.

Supergidrofobnaya mikroflyuidika

16 April 2015 in 11:30

O.I. Vinogradova (IFKhE im. A.N.Frumkina RAN i Fizicheskii fakul’tet MGU im. M.V.Lomonosova)

Supergidrofobnye materialy otkryli sovershenno novye napravleniya issledovanii s bol’shimi fundamental’nymi i prakticheskimi perspektivami. Issledovaniya etikh materialov byli, v osnovnom, sfokusirovany na ikh chrezvychaino plokhoi smachivaemosti vodoi. Sledstviya supergidrofobnosti dlya transportnykh yavlenii v mikro- i nanomasshtabe do sikh por ostayutsya maloizuchennymi. V svoem doklade ya budu obsuzhdat’, kak ispol’zovanie supergidrofobnykh poverkhnostei mozhet privesti k gigantskomu effektivnomu skol’zheniyu, «sverkhtekuchesti» vody v mikrokanalakh, snizheniyu gidrodinamicheskogo soprotivleniya, a takzhe kak takie poverkhnosti mogut byt’ ispol’zovany dlya sozdaniya novykh metodov separatsii mikrochastits i passivnogo peremeshivaniya zhidkostei.

Occurrence of flat bands in strongly correlated Fermi systems and high-Tc superconductivity of electron-doped compounds

26 February 2015 in 11:30

V.A. Khodel (Kurchatov Institute & Washington University)

We consider a class of strongly correlated Fermi systems that possess interaction-induced flat bands, pinned to the Fermi surface. We demonstrate that in such systems, the fundamental Landau equation, connecting the single-particle spectrum to the quasiparticle momentum distribution, fails. We propose a method, allowing to rectify drawbacks of Landau theory and, with the aid of the Pitaevskii identity, generalize equations obtained to apply the method to electron systems of solids. The emergent non-Fermi-liquid behavior, derived from the theory constructed, is compared with relevant experimental data on two-dimensional liquid He-3, heavy-fermion metals and electron-doped high-Tc compounds.

Topological Valley Currents in Gapped Dirac Materials

19 February 2015 in 11:30

L. Levitov (MIT)

Gapped 2D Dirac materials, in which inversion symmetry is broken by a gap-opening perturbation, feature a unique valley transport regime. The system ground state hosts dissipationless persistent valley currents existing even when topologically protected edge modes are absent or when they are localized due to edge roughness. Topological valley currents in such materials are dominated by bulk currents produced by electronic states just beneath the gap rather than by edge modes. Dissipationless currents induced by an external bias are characterized by a quantized half-integer valley Hall conductivity. The under-gap currents dominate magnetization and the charge Hall effect in a light-induced valley-polarized state.

Energeticheskii transport v sisteme vstrechnykh kraevykh kanalov i model’ Lattinzhera

29 January 2015 in 11:30

Vadim Khrapai (IFTT RAN)

Budut predstavleny rezul’taty nedavnego eksperimenta [1] po izucheniyu neravnovesnykh potokov energii mezhdu vstrechnymi kraevymi kanalami v rezhime kvantovogo effekta Kholla. Sistema iz dvukh takikh kanalov, razvyazannykh gal’vanicheski, no vzaimodeistvuyushchikh posredstvom kulonovskikh sil, yavlyaetsya pryamym analogom besspinovoi zhidkosti Lattinzhera [2] i ideal’no podkhodit dlya izucheniya energeticheskogo transporta. Original’nyi bolometricheskii podkhod k izmereniyu izbytochnogo potoka energii P v kraevom kanale pozvolil issledovat’ zavisimosti P ot tyanushchego napryazheniya i protyazhennosti otrezka lattinzherovskoi zhidkosti. Pokazano, chto protsess peredachi energii kolichestvenno soglasuetsya s kontseptsiei uprugogo rasseyaniya kollektivnykh vozbuzhdenii plotnosti na granichnykh tochkakh lattinzherovskogo otrezka, pri etom imeetsya vozmozhnost’ nepreryvnogo kontrolya parametra vzaimodeistviya i veroyatnosti rasseyaniya. Literatura: [1] M.G. Prokudina, S. Ludwig, V. Pellegrini, L. Sorba, G. Biasiol, V.S. Khrapai, Tunable non-equilibrium Luttinger liquid based on counter-propagating edge channels, Phys. Rev. Lett. 112, 216402 (2014). [2] Yuval Oreg and Alexander M. Finkel'stein, Interedge Interaction in the Quantum Hall Effect, Phys. Rev. Lett. 74, 3668 (1995).

Novoe v kvantovoi mekhanike. Neperiodicheskie odnozonnye potentsialy i ikh obobshcheniya

25 December 2014 in 11:30

V.E. Zakharov, D.V. Zakharov

O spektre odnomernogo statsionarnogo operatora Shredingera s neubyvayushchim na beskonechnosti ogranichennym po modulyu potentsialom izvestno dovol’no malo. Khorosho izvestny kvaziperiodicheskie mnogozonnye potentsialy, vyrazhayushchiesya v terminakh teta-funktsii Yakobi. Do nekotoroi stepeni izucheny sluchainye potentsialy, imeyushchie vpolne razryvnyi spektr. No eto ― ves’ma chastnye sluchai. Ob obshchikh neperiodicheskikh potentsialakh, imeyushchikh chisto nepreryvnyi, v prosteishem sluchae odnozonnyi, spektr, ranee nichego ne bylo izvestno. My stroim obshirnyi klass takikh potentsialov, parametrizuemyi dvumya polozhitel’nymi nepreryvnymi funktsiyami odnoi peremennoi. Sootvetstvuyushchie volnovye funktsii podchinyayutsya sisteme singulyarnykh integral’nykh uravnenii, kotoraya mozhet byt’ reshena chislenno. Fakticheski rech’ idet ob opisanii neperiodicheskikh sred, imeyushchikh zonnyi spektr, podobnyi spektru kristallov.

Shumy i statistika perenosa elektronov v kvantovykh provodnikakh pri nalichii peremennykh polei i vozmozhnosti sozdaniya odnochastichnykh izolirovannykh vozbuzhdenii

18 December 2014 in 11:30

G.B. Lesovik

V pervoi chasti doklada budet sdelan nebol’shoi obzor teoreticheskikh rabot po shumam i statistike perenosa v tselom. Zatem obsudim teoreticheskie raboty, v kotorykh byli opisany vozmozhnosti sozdaniya odnochastichnykh izolirovannykh vozbuzhdenii (govorya bolee tochno, vozbuzhdeniya neobychnoi pary elektron-dyrka pri pomoshchi impul’sa vektornogo potentsiala lorentsevskoi formy), ne zaputannykh za fermi more. Vo vtoroi chasti budet obsuzhdat’sya eksperiment gruppy Glattli (opublikovano v 2013 g., Nature), v kotorom anonsirovano nablyudenie sootvetstvuyushchikh vozbuzhdenii. Budut izlozheny argumenty v pol’zu togo, chto v etom eksperimente usloviya dlya sozdaniya sootvetstvuyushchikh vozbuzhdenii (i ikh registratsii) ne vypolnyayutsya. Tem ne menee v eksperimente opredelenno nablyudalos’ drugoe yavlenie, svyazannoe s katastrofoi ortogonal’nosti dlya fermi morya, pri opredelennykh formakh impul’sa.

Dissipation of turbulence in superfluid 4He in the limit of zero temperature

30 October 2014 in 11:30

Andrei Golov (School of Physics and Astronomy, The University of Manchester, UK)

We will review Manchester experiments on quantum turbulence in superfluid 4He generated by various means. The main focus is on the limit of zero temperatures, in which the turbulence is fully represented by tangled quantized vortex lines. In this regime, the dynamics of the vortex lines span length scales from the size of container to nearly atomic scale, at which energy is transmitted to phonons. A quantum cascade of energy, involving individual quantized vortex lines (and hence, having no analogs in classical turbulence), is necessary for the energy of large-scale flow to be transferred to the dissipative short scales. The processes maintaining the cascade are believed to be: hydrodynamic interactions of vortex lines, reconnections of vortex lines, interaction of excitations such as small vortex loops and Kelvin waves on vortex lines. The dissipative length scale can be increased (i.e. the quantum cascade curtailed) by increasing temperature above 0.4 K due to the scattering of thermal excitations by vortex lines. Three different means of generating turbulence will be discussed (each having an analog in classical turbulence, thus allowing comparison with classical results): (a) With the towed grid, we produce turbulence that is nearly homogeneous and isotropic. Studying the free decay allows the rate of dissipation to be quantified [6]. (b) An unsteady rotation of a square-shaped container allows to create anisotropic turbulence — that decays more slowly [1,5,6]. In the presence of the steady background rotation, the following phenomena are observed: steady polarization of vortex lines, non-zero threshold for turbulence onset, resonances of inertial waves [4]. (c) With an immersed jet of variable duration and intensity (created by a current of injected electrons), a cross-over from ultraquantum («non-structured» or «Vinen») turbulence to quasiclassical («structured» or «Kolmogorov») turbulence is observed [2,3]. (References: [1] P. M. Walmsley, A. I. Golov, H. E. Hall, A. A. Levchenko and W. F. Vinen, Dissipation of quantum turbulence in the zero-temperature limit, Phys. Rev. Lett. 99, 265302 (2007). [2] P. M. Walmsley and A. I. Golov, Quantum and quasiclassical types of superfluid turbulence, Phys. Rev. Lett. 100, 245301 (2008). [3] A. I. Golov, P. M. Walmsley, P. Tompsett, Charged Tangles of Quantized Vortices in Superfluid 4He, J. Low Temp. Phys. 161, 509-525 (2010). [4] P. M. Walmsley and A. I. Golov, Rotating quantum turbulence in superfluid 4He in the T=0 limit, Phys. Rev. B 86, 060518(RC) (2012). [5] Paul Walmsley, Dmitry Zmeev, Fatemeh Pakpour, and Andrei Golov, Dynamics of quantum turbulence of different spectra, PNAS 111 (Supplement 1) 4691-4698 (2014). [6] D. E. Zmeev, P. M. Walmsley, A. I. Golov, P. V. E. McClintock, S. N. Fisher, and W. F. Vinen, Turbulence in superfluid 4He generated by various means (in preparation).)

Electron-electron interaction effects in monotonic and oscillatory magnetotransport in 2D electron systems

23 October 2014 in 11:30

V.M. Pudalov (LPI)

Studying the oscillatory magnetorestance in crossed fields, we found that the product (m*TD) that determines damping of quantum oscillations, to the first approximation is equal in the majority and minority subbands even though the spin polarization degree amounts to about 66%. This result confirms theory predictions that the interaction takes place at high energies > EF rather than within narrow strip of energies EF ± T. To the next approximation, we revealed a difference in the damping factor of the two spin subbands, which causes skewness of the oscillation lineshape. The difference, quantified with the skew factor can be as high as 20%. The skew factor decreases as B or temperature grow, or B decreases; for low electron densities and high in-plane field the skew factor even changes sign. In contrast to the conventional theory, the product (m*TD) varies with perpendicular field and (nonmonotonically) with temperature. These dependencies explain notable scattering of the m*(n) values experimentally obtained under assumption of the T-independent (m*TD). The monotonic magnetoconductance in the in-plane field δσ(B,T) was found to scales in a sharp contrast to the theory predictions: whereas below a density dependent temperature T<T* it scales as theory predicted, (B2/T), at higher temperatures T>T*, it scales as (B2/T2). The latter dependence, hence, mimics the behavior anticipated for the low-temperature diffusive regime of interaction. These functional dependencies are at odd with interaction quantum corrections. The crossover temperature T*(n) correlates well with the inflection point at the strong σ(T) dependence in zero field, inherent for high mobility samples. Our data thus point at the existence of an energy scale T* beyond the EF. The results also call in question the previous attempts to exploit the parallel field MR as a tool to determine Fermi liquid coupling constants, F0a and γ2, and to plot the two-parameter phase diagrams for interacting and disordered 2D electron systems.

Vyvod pravila Borna iz unitarnosti kvantovoi evolyutsii

16 October 2014 in 11:30

G.B. Lesovik

Dlya togo, chtoby kvantovaya mekhanika byla zamknutoi teoriei (khotya by kak veroyatnostnaya teoriya), neobkhodimo ne postulirovat’ pravilo Borna, a imet’ sposob ego vyvoda iz pervykh printsipov, v chastnosti iz uravnenii dvizheniya (naprimer, uravneniya Shredingera). V opredelennoi stepeni eto sdelano v neskol’kikh stat’yakh, nachinaya so stat’i Doicha 1999 goda. My uprostili argumenty predydushchikh avtorov i v dannoi rabote pokazhem, kak vyvesti pravilo Borna, ispol’zuya to, chto v protsesse unitarnoi evolyutsii norma sostoyaniya ⟨Ψ|Ψ⟩ sokhranyaetsya. Imenno eto obstoyatel’stvo v konechnom schete vedet k tomu, chto veroyatnost’ sobytii v kvantovoi mekhanike opredelyaetsya kvadratom volnovoi funktsii. My takzhe korotko izlozhim argumenty v dukhe mnogomirovoi interpretatsii v pol’zu togo, chto kvantovaya mekhanika yavlyaetsya estestvennym obrazom veroyatnostnoi teoriei. Pri etom sluchainost’ poyavlyaetsya kak rezul’tat predstavleniya volny (volnovoi funktsii) pri pomoshchi diskretnogo ob’ekta — pribora, kotoryi mozhet detektirovat’ tol’ko odno iz vozmozhnykh znachenii dinamicheskoi peremennoi.

Kvantovye nizkoplotnostnye kody i nelokal’nye spinovye modeli

9 October 2014 in 11:30

Leonid Pryadko (Kaliforniiskii Universitet, Riversaid)

Lokal’nost’ — odin iz osnovopolagayushchikh printsipov postroeniya fizicheskikh modelei. Tak, v modeli Izinga, kazhdyi chlen v gamil’toniane mozhet sootvetstvovat’ svyazi mezhdu blizhaishimi sosedyami na zadannoi reshetke. Chto poluchitsya esli uslovie lokal’nosti opustit’? Ya otvechu na etot vopros na primere neuporyadochennykh spinovykh modelei opisyvayushchikh protseduru dekodirovaniya kvantovykh nizkoplotnostnykh kodov. Takim obrazom mogut byt’ polucheny kak traditsionnye lokal’nye spinovye modeli (model’ Izinga, kalibrovochnaya model’ Z2), tak i netrivial’nye nelokal’nye modeli kotorye ne byli izucheny ranee. Uporyadochennaya faza v takikh modelyakh sootvetstvuet nalichiyu glubokogo minimuma svobodnoi energii; “post-topologicheskimi” vozbuzhdeniyami yavlyayutsya protyazhennye defekty obobshchayushchie ponyatie domennoi stenki. Izvestno neskol’ko konstruktsii kvantovykh nizkoplotnostnykh kodov s konechnoi skorost’yu. V sootvetstvuyushchikh spinovykh modelyakh chislo razlichnykh tipov defektov eksponentsial’no veliko. V takikh modelyakh vozmozhen chisto entropiinyi fazovyi perekhod, kogda analog poverkhnostnogo natyazheniya dlya defektov kazhdogo tipa ostaetsya konechnym. [A. A. Kovalev and L. P. Pryadko, “Spin glass reflection of the decoding transition for quantum error correcting codes”, arXiv:1311.7688]

Anderson localization models on Bethe Lattice and Random Regular Graphs: is the extended state always ergodic?

25 September 2014 in 11:30

V.E. Kravtsov (Abdus Salam ICTP, Trieste)

Entropy measurements in 2D systems

18 September 2014 in 11:30

A.Yu. Kuntsevich (LPI)

In this talk I am going to discuss the experimental technique to measure entropy-per-electron in gated 2D systems, the we recently developed. We applied this technique to study magnetooscillations in Si and GaAs-based 2D systems and zero-perpendicular field effects. The latter originate from: (i) non-degeneracy of the Fermi system and (ii) electron-electron correlations. In particular, we explore enhanced effective mass in non-degenerate strongly correlated plasma regime EF < T < U (where U is the Coulomb energy e2 / ‹ r ›).

Can liquid water unmix?

26 June 2014 in 11:30

M.A. Anisimov (University of Maryland, USA)

Twenty years ago Poole et al. suggested that the anomalous properties of supercooled water may be caused by a critical point that terminates a line of metastable liquid-liquid separation of lower-density and higher-density water [1]. This phenomenon is viewed as “water’s polyamorphism”. In this presentation I explain how supercooled water can unmix and describe a phenomenological model in which liquid water at low temperatures is viewed as athermal “solution” of two hydrogen-bond network structures with different entropies and densities [2,3]. Alternatively to lattice-gas models, in which fluid phase separation is driven by energy, the phase transition in the athermal two-state water is driven by entropy upon increasing the pressure, while the critical temperature is defined by the “reaction” equilibrium constant. The order parameter, the extent of “reaction”, coupled with density and entropy, while the ordering field is a combination of temperature and pressure. The model gives the best representation of all available experimental data for supercooled ordinary and deuteraded water and predicts the location of density maxima at the locus of a near-constant fraction of the lower-density structure. I will also discuss the lessons we can learn on real water from simulations of popular water-like models, such as mW and ST2 [4,5]. ( References: [1] P. H. Poole, F. Sciortino, U. Essmann, and H. E. Stanley, Nature 360, 324 (1992). [2] C. E. Bertrand and M. A. Anisimov, Phys. Chem. B 115, 14099 (2011). [3] V. Holten and M. A. Anisimov, Sci. Rep. 2, 713 (2012). [4] V. Holten, D. T. Limmer, V. Molinero, and M. A. Anisimov, J. Chem. Phys. 138, 174501, (2013). [5] V. Holten, J. C. Palmer, P. H. Poole, P. G. Debenedetti, and M. A. Anisimov, J. Chem. Phys. 140, 104502 (2014). )

New results on dark energy in the early and present Universe and the observational status of the inflationary scenario

19 June 2014 in 11:30

Alexei A. Starobinsky

The measurement of a small deviation of the primordial spectrum of scalar (density) perturbations in the Universe from the exactly flat (or, Harrison-Zeldovich) one in the WMAP and Planck experiments confirms the general prediction of the early Universe scenario with the de Sitter (inflationary) stage preceding the radiation dominated stage (the hot Big Bang) and strongly restricts the class of viable inflationary models. The announced discovery of primordial gravitational wave background through the measurement of the B-mode of linear polarization of the cosmic microwave background radiation (CMB) in the range of multipoles l = (50 – 150) in the BISEP2 experiment [1] confirms another general prediction [2] of this scenario, as well as produces the direct evidence for the existence of a very strongly curved space-time in the past of our Universe and the necessity of quantization of gravitational waves. Still the BISEP2 result is partially contaminated by foregrounds (mainly by polarized galactic dust emission) and requires confirmation of its blackbody character by measurements at other wavelengths. Moreover, comparison of BISEP2 data with the temperature and E-mode polarization data earlier obtained in the WMAP and Planck experiments shows that the inflationary stage is not so simple and may not be described by a one-parametric model. In particular, the primordial spectrum of scalar perturbations generated during inflation is not of a power-law form [3], mainly due to the ~10% depression of the angular anisotropy power spectrum in the multipole range 20 < l < 40. A class of models describing this feature which implies existence of some scale (i.e. new physics) during inflation is proposed [4]. Furthermore, account of additional wiggles in the spectrum at l = 22 and 40 requires further complication of the inflaton potential [5] by introducing sharp features of the type suggested by previous studies [6]. ( References: [1] P.A.R. Ade et al. [BISEP2 Collaboration], arxiv:1403.3985. [2] A.A. Starobinsky, JETP Lett. 30, 682 (1979). [3] D.K. Hazra, A. Shafieloo, G.F. Smoot, A.A. Starobinsky. Ruling out the power-law form of the scalar primordial spectrum. JCAP, in press (2014); arXiv:1403.7786. [4] D.K. Hazra, A. Shafieloo, G.F. Smoot, A.A. Starobinsky. Whipped inflation. ArXiv:1404.0360. [5] D.K. Hazra, A. Shafieloo, G.F. Smoot, A.A. Starobinsky. Wiggly whipped inflation. ArXiv:1405.2012. [6] A.A. Starobinsky, JETP Lett. 55, 489 (1992). )


Unikal’nye elektromekhanicheskie svoistva kvaziodnomernykh provodnikov s volnoi zaryadovoi plotnosti

24 April 2014 in 11:30

V.Ya. Pokrovsky (IRE RAS)

Rech’ poidyot o kvaziodnomernykh provodnikakh, v kotorykh nizhe temperatury paierlsovskogo perekhoda voznikaet volna zaryadovoi plotnosti (VZP). Bol’shinstvo takikh soedinenii predstavlyayut soboi nitevidnye kristally. Budet rasskazano o sleduyushchikh effektakh: snizhenii uprugikh modulei pri sryve VZP s primesei, izmenenii dliny obraztsov pod deistviem elektricheskogo polya ili termotsiklirovaniya, neodnorodnoi deformatsii obraztsov v elektricheskom pole. Naibolee podrobno budet rasskazano o deformatsii krucheniya, v chastnosti, o krutil’nykh kolebaniyakh. Vse perechislennye effekty mozhno kachestvenno opisat’ na yazyke uprugogo vzaimodeistviya VZP s reshyotkoi kristalla. Odnako est’ osnovaniya polagat’, chto takoe opisanie — chrezmerno uproshchyonnoe. [Literatura: V.Ya. Pokrovskii, S.G. Zybtsev, M.V. Nikitin, I.G. Gorlova, V.F. Nasretdinova, S.V. Zaitsev-Zotov. «Vysokochastotnye, „kvantovye“ i elektromekhanicheskie effekty v kvaziodnomernykh kristallakh s volnoi zaryadovoi plotnosti», UFN, 183, 33 (2013).]

Kvantovaya interferentsiya dirakovskikh fermionov v nanoperforirovannom grafene

17 April 2014 in 11:30

Yu.I. Latyshev (IRE im. V.A. Kotel'nikova RAN)

Rassmotreny nedavnie eksperimenty po effektu Aaronova-Boma na provodyashchikh kraevykh sostoyaniyakh, lokalizovannykh vokrug nanootverstii v nanoperforirovannovannykh grafenovykh strukturakh [1], a takzhe eksperimenty po nablyudeniyu orbital’nogo kvantovaniya kraevykh dirakovskikh fermionov pri ikh dvizhenii vokrug nanootverstiya v nulevom magnitnom pole [2]. Rezul’taty eksperimentov oboikh tipov soglasuyutsya s teoriei kraevykh sostoyanii tammovskogo tipa v grafene. Literatura: [1] Yu.I. Latyshev et al., cond-mat arXiv : 1310.0991. [2] Yu.I. Latyshev, A.P. Orlov, A.V. Frolov et al., JETP Lett., 98, 214 (2013).

Fazovaya diagramma tsepochki bezdissipativnykh dzhozefsonovskikh kontaktov

3 April 2014 in 11:30

L.B. Ioffe

Perekhod mezhdu fermi- i boze-statistikoi v 2-mernoi sisteme

27 March 2014 in 11:30

Andrey Turlapov (IPF RAN, Nizhnii Novgorod)

V edinom eksperimente proiskhodit perestroika sistemy mezhdu bozonnym i fermionnym sostoyaniem. Eksperiment vypolnen s gazom fermi-atomov litiya-6 s s-vzaimodeistviem pri temperature ~ 10 nK. Pri roste vzaimodeistviya atomy ob’edinyayutsya v 2-atomnye molekuly bozony. 2-mernost’ dostignuta plotnym uderzhaniem vdol’ odnogo iz napravlenii. Chistota ul’trakholodnoi atomnoi sistemy dayot vozmozhnost’ sravnivat’ dannye s teoreticheskimi modelyami, postroennymi iz pervykh printsipov, bez svobodnykh parametrov. V chastnosti, naidennoe nami otlichie davleniya slabo vzaimodeistvuyushchego fermi-gaza ot predskazaniya dlya odnorodnoi fermi-zhidkosti mozhet stat’ stimulom dlya razvitiya teorii 2-mernykh mezoskopicheskikh sistem. Izmereniya v sil’no vzaimodeistvuyushchem gaze, mezhdu fermi- i boze-rezhimami, pokazyvayut neobkhodimost’ ucheta 3-mernogo kharaktera vzaimodeistvii pri modelirovanii gaza s 2-mernoi kinematikoi.

Spinful fermionic ladders at incommensurate filling: Phase diagram, local perturbations, and ionic potentials

24 February 2014 in 10:00

Boris Narozhny (Karlsruhe Institute of Technology, Germany)

We study the effect of external potential on transport properties of the fermionic two-leg ladder model. The response of the system to a local perturbation is strongly dependent on the ground state properties of the system and especially on the dominant correlations. We categorize all phases and transitions in the model (for incommensurate filling) and introduce ’’hopping-driven transitions’’ that the system undergoes as the inter-chain hopping is increased from zero. We also describe the response of the system to an ionic potential. The physics of this effect is similar to that of the single impurity, except that the ionic potential can affect the bulk properties of the system and in particular induce true long range order.

Nonequilibrium transport in high Landau levels of 2D systems: recent developments

13 February 2014 in 15:00

M.A. Zudov (School of Physics and Astronomy, University of Minnesota, USA)

Over the last decade, magneto transport in very high Landau levels of high-mobility 2D electron systems (2DES) hosted in GaAs/AlGaAs quantum wells revealed a variety of new intriguing phenomena. Two prime examples of these phenomena are microwave-induced resistance oscillations (MIRO) and associated zero-resistance states which emerge when a high-mobility 2DES is irradiated by microwave radiation. Another prominent effect is Hall field-induced resistance oscillations (HIRO) which appear in differential resistivity when a system is driven by a dc field. Both MIRO and HIRO originate from inter-Landau level transitions owing to photon absorption and/or impurity scattering. In this talk I will discuss our recent experimental studies on i) Shubnikov-de Haas oscillations in conventional high-mobility 2D electron gas in GaAs/Al0.24Ga0.76As quantum wells irradiated by sub-terahertz (up to 0.4 THz) radiation, ii) MIRO and HIRO in AlxGa1-xAs/Al0.24Ga0.76As quantum wells with x up to 0.0078, and, finally, iii) observation of MIRO in a moderate-mobility 2D hole gas hosted in a pure Ga/Si0.2Ge0.8 quantum well.

Probing interactions with thermal transport

6 February 2014 in 11:30

Karen Michaeli (Weizmann Institute of Science)

Thermal and thermoelectric conductivities are ideal probes of interaction effects in correlated electron systems. This is because, in contrast to an electric current, a heat current can be transmitted also by neutral quasiparticles. For instance, energy can be carried by excitations that mediate interactions between other quasiparticles. In my talk I will present two examples of the dramatic effect of interactions on thermal and thermoelectric transport phenomena. The first is the Nernst effect in the vicinity of the superconducting phase transition. I will discuss the anomalous behavior of the Nernst effect near the magnetic-field-induced quantum critical phase transition. The second example is thermal conductivity in spin liquids. Spin liquids can form in the vicinity of the Mott metal-insulator transition when the charge is gapped while the spin degrees of freedom strongly fluctuate. These low energy excitations, dubbed spinons, can conduct heat. The spinons also exhibit a magnetic interaction that leads to non-Fermi liquid behavior. I will show that even in the absence of disorder this strong interaction provides an efficient relaxation mechanism for the heat current.

Composite fermion state of spin-orbit coupled bosons

21 November 2013 in 11:30

Alex Kamenev (Univ. of Minnessota, USA)

Recent experiments in cold atomic gases produced bosons with spin-orbit coupling. Their dispersion relation exhibits a minimum along a circle in the momentum space. It poses a problem of Bose condensation of particles with the degenerate minimum of the kinetic energy. We argue that in 2D the Bose condensation does not occur. Instead, a correlated state, similar to Laughlin liquid in the fractional quantum Hall effect, is formed.

Electrodynamics of strongly disordered superconductors

14 November 2013 in 11:30

T. M. Klapwijk

Superconductors with a high resistivity in the normal state are of interest for experiments on quantum phase slip devices and radiation-detection, such as hot-electron bolometers and, more recently, microwave kinetic inductance detectors. In addition they are excellent candidate-materials to be used in experiments, which require a superconductor in the presence of a high magnetic field, such as in experiments which combine semiconductors with superconductors. These materials have also been of interest, for several decades already, to demonstrate and analyze the so-called superconductor-insulator transition. Examples are NbN, NbTiN, TiN, MoN, etc. The new interest provides new experimental data to be understood and stimulates further theoretical analysis. In my talk I will present an overview of the new applications as well as new experimental data on the electrodynamics originating from our work with superconducting resonators. [1] E. F. C. Driessen, P. C. J. J. Coumou, R. R. Tromp, P.J. de Visser, and T. M. Klapwijk, Phys. Rev. Lett. 167, 360 (2012); [2] P. C. J. J. Coumou, E. F. C. Driessen, J. Bueno, C.Chapelier, and T.M. Klapwijk, Phys. Rev. B 88, 180505 R, (2013).

Anderson localization at the edge of 2D topological insulator

7 November 2013 in 11:30

Vladimir Yudson (Institute for Spectroscopy RAS, Troitsk)

Spins of chiral electrons moving along the 1D helical edge of a 2D topological insulator are tightly bound to their momenta. This suppresses electron backscattering by the usual potential disorder and protects the system from Anderson localization. We study effects of electron interactions with a disordered chain of spin (Kondo) impurities located near the helical edge. Assuming the electron-spin couplings of random anisotropies, we map this system to the problem of the pinning of the charge density wave by the disordered potential. This mapping shows that anisotropic couplings of chiral electrons with spin impurities lead to Anderson localization of the helical edge states. [B.L. Altshuler, I.L. Aleiner, and V.I. Yudson, Phys. Rev. Lett. 111, 086401 (2013)]

Hydrodynamics of active polar fluids

14 October 2013 in 11:30

Prof. K. Kruse (University of Saarlandes, Germany)

Many vital cellular processes are driven by the cytoskeleton, a network of filamentous polymers present in every living cell. The filaments have two structurally different ends making them polar objects and interact with a large number of associated proteins. To fulfill its various tasks, the cytoskeleton is kept out of thermodynamic equilibrium by energy that is fed into the system on the level of its constituents. Notably, the assembly of cytoskeletal filaments and the action of molecular motors that can generate stresses in the network depend on the local release of chemical energy. From a physical point of view, the cytoskeleton can be classified as an active polar fluid. In this talk, we will present a hydrodynamic description of active polar fluids. Using this theory, we will analyze the spontaneous emergence of flows as well as the stability of topological point defects. If time permits, we will also discuss the actin cortex as an example of a biologically relevant structure. We propose to view its formation as an active analogue of a (pre-)wetting transition.

Conductivity of suspended graphene at the Dirac point

3 October 2013 in 11:30

V.Yu. Kachorovskii (A.F. Ioffe Physical-Technical Institute)

We study transport properties of clean suspended graphene at the Dirac point. In the absence of the electron-electron interaction, the main contribution to resistivity comes from interaction with flexural (out-of-plane deformation) phonons. We find that the phonon-limited conductivity scales with the temperature as T−η, where η is the critical exponent (equal to ≈ 0.7 according to numerical studies) describing renormalization of the flexural phonon correlation functions due to anharmonic coupling with the in-plane phonons. The electron-electron interaction induces an additional scattering mechanism and also affects the electron-phonon scattering by screening the deformation potential. We demonstrate that the combined effect of both interactions results in a conductivity that can be expressed as a dimensionless function of two temperature-dependent dimensionless constants, G[T] and Ge[T], which characterize the strength of electron-phonon and electron-electron interactions, respectively. We also discuss the behavior of conductivity away from the Dirac point as well as the role of the impurity potential and demonstrate and compare our predictions with available experimental data.

Coulomb drag in graphene near the Dirac point

5 September 2013 in 11:30

I.V. Gornyi (Karlsruhe Institute of Technology and Ioffe Physical Technical Institute)

We study Coulomb drag in graphene near the Dirac point, focusing on the regime of interaction-dominated transport. We establish a novel, graphene-specific mechanism of Coulomb drag based on fast interlayer thermalization, inaccessible by standard perturbative approaches. Using the quantum kinetic equation framework, we derive a hydrodynamic description of transport in double-layer graphene in terms of electric and energy currents. In the clean limit, the drag becomes temperature independent. In the presence of disorder the drag coefficient at the Dirac point remains nonzero due to higher-order scattering processes and interlayer disorder correlations. At low temperatures (diffusive regime) these contributions manifest themselves in the peak in the drag coefficient centered at the neutrality point with a magnitude that grows with lowering temperature. Motivated by recent experiments, further we propose a phenomenological model of the magnetodrag in graphene. Near charge neutrality, each of the layers contains two kinds of carriers (quasiparticles) with opposite electric charge — electrons and holes, such that the quasiparticle (or energy) and electric currents become noncollinear in the presence of external magnetic field. Precisely at the Dirac point, these currents are orthogonal to each other, giving rise to a giant magnetodrag. The sign of the drag resistance depends on the strength of the electron-phonon interaction, as well as on the geometry of the sample. Away from the Dirac point, the quasiparticle current acquires a component in the direction of the electric current, leading to non-zero Hall drag. The predictions of the model agree with the experimental data in weak magnetic fields measured in double-layer graphene/boron-nitride heterostructures.

Exciton many-body effects and Bose-Einstein condensation

23 May 2013 in 11:30

Monique Combescot (Institut des NanoSciences de Paris, Université Pierre et Marie Curie, CNRS)

In order to describe physical effects involving excitons in a convenient way, I will first introduce the «Shiva and Kali diagrams» which visualize many-body effects between composite quantum particles. I will also provide the theoretical grounds on which they are based. These diagrams will be used to present some non-linear optical effects involving virtual excitons coupled to unabsorbed photons such as spin precession and teleportation, Faraday rotation and oscillation, exciton trapping and so on... In a second part, I will turn to exciton BEC. I will explain (i) why excitons must condense into a linearly polarized dark state — which probably is the reason why this condensation has been missed for decades — (ii) how under a density increase, the dark condensate acquires a bright component, (iii) why a phase separation can take place between an exciton gas and an electron-hole plasma, the dense phase possibly being a BCS condensate of «electron-hole Cooper pairs». I will end by showing a few very recent experimental data, taken by François Dubin and his group, which evidence the dark exciton Bose-Einstein condensate. (References: [1] M. COMBESCOT, O. BETBEDER-MATIBET, F. DUBIN, The many-body physics of composite bosons, Physics Report 463, 215 (2008). [2] M. COMBESCOT, O. BETBEDER-MATIBET, General many-body formalism for composite quantum particles, Phys. Rev. Lett. 104, 206404, (2010). [3] M. COMBESCOT, S. SHIAU, Y. CHANG, Finite temperature formalism for composite quantum particles, Phys. Rev. Lett. 106, 206403 (2011). [4] M. COMBESCOT, O. BETBEDER-MATIBET, R. COMBESCOT, Bose-Einstein condensation in semiconductors: the key role of dark excitons, Phys. Rev. Lett. 99, 176403, (2007). [5] R. COMBESCOT, M. COMBESCOT, «Gray» BCS condensate of excitons and internal Josephson effect, Phys. Rev. Lett. 109, 026401 (2012). [6] M. ALLOING, M. BEIN, D. FUSTER, Y. GONZALES, L. GONZALES, R. COMBESCOT, M. COMBESCOT, F. DUBIN, Evidence for a Bose-Einstein condensate of excitons, arXiv:1304.4101.)

Coherent Back Scattering and Anderson Localization of Ultra Cold Atoms

25 April 2013 in 11:30

Alain Aspect (Institut d’Optique, Palaiseau, France)

We use ultra cold atoms in a disordered potential created with a laser speckle, to study Anderson Localization (AL) and Coherent Back Scattering (CBS). Localization has been observed in 1D and 3D, and 2D experiments are promising. Theory supports the conclusion that what we observe is AL, but a direct evidence of the role of coherence is desirable. Recently, we have observed CBS, an indisputable coherent effect in quantum transport, related to the first order manifestation of localization (weak localization).

Spin-fluktuatsionnyi mekhanizm sparivaniya v sverkhprovodnikakh na osnove zheleza

18 April 2013 in 11:30

M.M. Korshunov (Institut fiziki im. L.V. Kirenskogo SO RAN, Krasnoyarsk)

Sverkhprovodniki na osnove zheleza, otkrytye v 2008 godu, predstavlyayut soboi novyi klass vysokotemperaturnykh sverkhprovodnikov s velichinoi kriticheskoi temperatury do 55K. Otnosyashchiesya k etomu klassu pniktidy i khal’kogenidy obladayut nizkotemperaturnymi svoistvami, var’iruyushchimisya ot soedineniya k soedineniyu. I khotya nakopleno mnozhestvo eksperimental’nykh dannykh, odnoznachnykh otvetov na takie fundamental’nye voprosy, kak simmetriya parametra poryadka, ego struktura, i mekhanizm sverkhprovodyashchego sparivaniya, eshchyo net. V doklade budet rassmotreno sovremennoe sostoyanie etikh problem i pokazano, chto vidimuyu neuniversal’nost’ mozhno ob’yasnit’ v ramkakh spin-fluktuatsionnoi teorii sparivaniya, prinimaya vo vnimanie osobennosti elektronnoi struktury pniktidov i khal’kogenidov [1,2]. [1] P.J. Hirschfeld, M.M. Korshunov, I.I. Mazin, Rep. Prog. Phys. 74, 124508 (2011). [2] S. Maiti, M.M. Korshunov, A.V. Chubukov, Phys. Rev. B 85, 014511 (2012).

Tochno reshaemaya model’ elektronnogo interferometra Makha‒Tsendera v rezhime tselochislennogo kvantovogo effekta Kholla

28 March 2013 in 11:30

Dmitry Bagrets (Institute for Theoretical Physics, University of Cologne, Germany)

V doklade budut rassmotreny neravnovesnye svoistva elektronnogo interferometra Makha-Tsendera (IMTs), kotoryi realizuetsya na osnove odnomernykh kraevykh sostoyanii v rezhime tselochislennogo kvantovogo effekta Kholla. Mnogochislennye eksperimenty po izucheniyu transportnykh svoistv IMTs ukazyvayut na nalichie sil’nogo mezhelektronnogo vzaimodeistviya v etikh mezoskopicheskikh strukturakh. Pri nizkikh temperaturakh nablyudaemaya zavisimost’ vidimosti interferometra ot vneshnego napryazheniya opisyvaetsya sil’no ostsilliruyushchei funktsiei s glubokimi minimumami, pri etom period ostsillyatsii opredelyaetsya obratnym vremenem proleta elektrona cherez plecho IMTs, a amplituda ostsillyatsii zatukhaet s rostom napryazheniya. Dannuyu zavisimost’ printsipial’no nevozmozhno ob’yasnit’ na osnove odnochastichnoi teorii Byuttikera-Beenakkera. Dlya opisaniya neobychnykh svoistv IMTs predlozhena netrivial’naya tochno reshaemaya model’, kotoraya zadaetsya koeffitsientami prozrachnosti dvukh kvantovykh kontaktov, obrazuyushchikh interferometr, i zaryadovoi energiei, opisyvayushchei dal’nodeistvuyushchee kulonovskoe vzaimodeistvie. Esli poslednee ogranicheno tol’ko vnutrennei oblast’yu interferometra, to zadacha dopuskaet tochnoe reshenie metodom neravnovesnoi bozonizatsii pri proizvol’nom tselochislennom faktore zapolneniya. V predele sil’nogo vzaimodeistviya zadacha IMTs okazyvaetsya tesno svyazannoi s zadachei o statistike perenosa zaryada v kvantovykh provodnikakh i s asimptoticheskimi kharakteristikami opredelitelei obobshchennykh matrits Tyoplitsa. Netrivial’naya ostsilliruyushchaya zavisimost’ vidimosti ot napryazheniya est’ proyavlenie mnogochastichnoi kvantovoi interferentsii, pri kotoroi dve glavnye amplitudy rasseyaniya, dayushchie osnovnoi vklad v provodimost’ Aaronova-Boma, imeyut fazovyi sdvig lineinyi po napryazheniyu.

Dvumernyi polumetall v shirokikh kvantovykh yamakh HgTe: Magnitotransport i energeticheskii spektr

21 March 2013 in 11:30

G.M. Min’kov (IFM UrO RAN), A.A. Sherstobitov, A.V. Germanenko, O.E. Rut, S.A. Dvoretskii, N.N. Mikhailov

Nesmotrya na ochen’ intensivnye issledovaniya, v poslednie 10 let, dvumernykh nositelei v kvantovykh yamakh na osnove besshchelevogo poluprovodnika HgTe, predstavleniya ob energeticheskom spektre, osobenno valentnoi zony, ostayutsya ochen’ protivorechivymi. V nastoyashchem doklade ya predstavlyayu rezul’taty issledovanii magnitotransportnykh effektov v MDP strukturakh s 20 nm kvantovoi yamoi HgTe v shirokom intervale kontsentratsii elektronov i dyrok. Sovmestnyi analiz polozheniya minimumov ρkhkh ostsillyatsii Shubnikova de Gaza, perioda ostsillyatsii i khollovskoi kontsentratsii, effektivnoi massy dyrok, naidennoi iz temperaturnykh zavisimostei ostsillyatsii, pozvolil rekonstruirovat’ spektr valentnoi zony pri kvaziimpul’sakh k > 8*105 sm-1. Uzhe eti rezul’taty pokazyvayut radikal’noe otlichie ot spektra, rasschitannogo v ramkakh kP modeli. Energeticheskii spektr pri k > 8*105 sm-1 byl otsenen iz analiza zavisimosti elektronnoi, electron-like i dyrochnoi kontsentratsii, naidennykh iz analiza magnitopolevykh zavisimostei ρkhkh i ρkhy v oblasti provodimosti dvumya tipami nositelei. Opredelennyi eksperimental’no zakon dispersii valentnoi zony kak pri malykh k, tak i pri bol’shikh, radikal’no otlichaetsya ot teoreticheski rasschitannogo. Obsuzhdayutsya soglasie s eksperimental’nymi rezul’tatami drugikh rabot i vozmozhnye prichiny otlichiya ot teorii.

Effekty aksial’noi anomalii v magnitnom pole

7 March 2013 in 11:30

A. Gorsky (ITEP)

Aksial’naya anomaliya privodit k ryadu interesnykh effektov v magnitnom pole. Budet rassmotren kiral’nyi magnitnyi effekt v plotnoi srede, novye bezmassovye vozbuzhdeniya — kiral’nye magnitnye volny i anomal’noe rasshcheplenie nulevogo zvuka v magnitnom pole.

Magnitnye nanostruktury s nekomplanarnym raspredeleniem namagnichennosti

21 February 2013 in 11:30

A.A. Fraerman (IPM RAS, Nizhniy Novgorod)

Dlya ferromagnetikov s nekomplanarnym raspredeleniem namagnichennosti predskazan ryad neobychnykh transportnykh i opticheskikh yavlenii, takikh kak «topologicheskii» vklad v khollovskuyu provodimost’ [Ya. Aharonov, A. Stern, Phys. Rev. Lett. 69, 3953 (1992)], diodnyi i fotogal’vanicheskii effekty [A.A. Fraerman, UFN 182, 1345 (2012)]. V doklade, v ramkakh fenomenologicheskogo i mikroskopicheskogo (s-d model’) podkhodov, obsuzhdayutsya mekhanizmy vozniknoveniya nevzaimnykh transportnykh yavlenii v nekomplanarnykh ferromagnetikakh. Predstavleny rezul’taty eksperimentov po sozdaniyu spiral’nykh, vikhrevykh i antivikhrevykh raspredelenii namagnichennosti, dlya kotorykh ukazannye effekty mogut nablyudat’sya.

Vliyanie zeemanovskogo rasshchepleniya na popravku k provodimosti ot elektron-elektronnogo vzaimodeistviya (eksperiment)

20 December 2012 in 11:30

A.Yu. Kuntsevich (LPI RAS)

Dvumernye elektronnye sistemy nizkoi plotnosti pri nizkikh temperaturakh demonstriruyut sil’noe polozhitel’noe magnitosoprotivlenie (MS) v parallel’nom pole, svyazannoe so spinovoi stepen’yu svobody. Nesmotrya na ryad predlozhennykh modelei, dannoe yavlenie daleko ne ponyato. Odnim iz vozmozhnykh mekhanizmov MS yavlyaetsya diffuzionnaya popravka ot elektron-elektronnogo vzaimodeistviya (EEP) [Lee, Ramakrishnan (1982)]. V nastoyashchei rabote my opredelyaem EEP iz odnovremennykh izmerenii ρxxρxy v razuporyadochennoi dvumernoi elektronnoi sisteme v Si v naklonnom magnitnom pole. Naklon magnitnogo polya pozvolyaet razdelit’ spinovye i orbital’nye effekty. V chastnosti, my pokazyvaem, chto v bol’shikh polyakh BB > T EEP: (i) zavisit ot modulya magnitnogo polya, a ne ot napravleniya, kak i dolzhno byt’ v sisteme s izotropnym g-faktorom; (ii) yavlyaetsya lineinoi po ln(B) i ln(T) kak i predskazyvaet teoriya. Naidennaya malaya popravka ne v sostoyanii ob’yasnit’ sil’nogo MS v parallel’nom pole, nablyudaemogo v Si dvumernykh sistemakh. Drugimi nablyudeniyami, ne soglasuyushchimisya s teoriei kvantovykh popravok, yavlyayutsya: 1) podavlenie polozhitel’nogo MS v parallel’nom pole nekvantuyushchim perpendikulyarnym polem; 2) nelineinoe po polyu khollovskoe soprotivlenie v malykh polyakh. Takim obrazom, dazhe v oblasti bol’shikh provodimostei, gde dolzhna byt’ primenima teoriya kvantovykh popravok, v dvumernoi elektronnoi sisteme v Si imeyutsya neob’yasnennye yavleniya.

Cantor sets and Chalker’s scaling: a simple picture of critical eigenfunction statistics

13 December 2012 in 11:30

Vladimir Kravtsov (ICTP, Trieste, Italy)

Multifractality of critical eigenstates in disordered conductors and superconductors is becoming an experimental issue. One of the key points is the critical enhancement of interaction matrix elements described by the Chalker’s scaling. In this work we show that the Chalker’s scaling is a simple consequence of the spectrum of local probe (like STM) which at criticality exhibits a Cantor set structure. We review the three-fold classification of spectra used by mathematicians and show their relation with the three types of local spectra.

Spin of superconducting quasiparticles

6 December 2012 in 11:30

Yu.V. Nazarov (Delft University of Technology, Netherlands)

We review the recent theoretical and experimental research that concerns the spin of superconducting quasiparticles and its possible use in the quantum manipulation context. We propose and theoretically investigate spin superconducting qubits. Spin superconducting qubit consists of a single spin confined in a Josephson junction. We show that owing to spin-orbit interaction, superconducting difference across the junction can polarize this spin. We demonstrate that this enables single qubit operations and more complicated quantum gates, where spins of different qubits interact via a mutual inductance of superconducting loop where the junctions are embedded. Recent experimental realizations of Josephson junctions made of semiconductor quantum dots in contact with superconducting leads have shown that the number of electrons in the quantum dot can be tuned by a gate voltage. Spin superconducting qubit is realized when the number of electrons is odd. We discuss the qubit properties at phenomenological level. We present a microscopic theory that enables us to make accurate estimations of the qubit parameters by evaluating the spin-dependent Josephson energy in the framework of fourth-order perturbation. We interpret a recent pioneering experiment [Zgirski M. et al., Phys. Rev. Lett., 106 (2011) 257003] on quasiparticle manipulation in a superconducting break junction in terms of spin blockade drawing analogy with spin qubits. We propose a novel qubit design that exploits the spin state of two trapped quasiparticles. We detail the coherent control of all four spin states by resonant quantum manipulation and compute the corresponding Rabi frequencies. The read-out technique is based on the spin-blockade that inhibits quasiparticle recombination in triplet states. We provide extensive microscopic estimations of the parameters of our model.

Probabilistic approach to Richardson equations

18 October 2012 in 11:30

W.V. Pogosov (Institute for Theoretical and Applied Electrodynamics RAS, Moscow)

Gamil’tonian teorii Bardina-Kupera-Shriffera yavlyaetsya tochno reshaemym. Eto reshenie opredelyaetsya naborom energiepodobnykh velichin, kotorye udovletvoryayut sisteme nelineinykh algebraicheskikh uravnenii, nazyvaemykh uravneniyami Richardsona. Reshenie etikh uravnenii dlya obshchego sluchaya yavlyaetsya otkrytoi zadachei. Zametim, chto uravneniya Richardsona mogut byt’ vyvedeny i s ispol’zovaniem tekhniki algebraicheskogo anzatsa Bete. Izvestno, chto uravneniya Richardsona obladayut elektrostaticheskoi analogiei. A imenno, resheniya uravnenii ekvivalentny polozheniyam ravnovesiya svobodnykh zaryadov na ploskosti, ottalkivayushchikhsya drug ot druga i vzaimodeistvuyushchikh s vneshnim elektrostaticheskim polem. V rabote predlozhen novyi podkhod k resheniyu uravnenii Richardsona. Vmesto neposredstvennogo otyskaniya polozhenii ravnovesiya vvoditsya «veroyatnost’» naiti sistemu zaryadov v dannoi konfiguratsii pri dostatochno nizkoi «temperature». «Veroyatnost’» opredelyaetsya funktsiei, skhozhei s volnovoi funktsiei Laflina dlya drobnogo kvantovogo effekta Kholla. Dalee, polozhenie tsentra mass sistemy zaryadov rekonstruiruetsya s pomoshch’yu metodov integrirovaniya putem vvedeniya «statsummy», zadannoi integralom tipa Sel’berga. Integraly takogo tipa figuriruyut v konformnoi teorii polya i teorii sluchainykh matrits. V rabote provedeny analiticheskie raschety dlya osnovnogo sostoyaniya sistemy v termodinamicheskom predele, dlya kotorogo podtverzhdeno soglasie so srednepolevymi predskazaniyami BKSh, a takzhe predstavleny nekotorye rezul’taty dlya sistem proizvol’nogo razmera. Podkhod mozhet byt’ poleznym i dlya resheniya drugikh tipov uravnenii Bete-anzatsa.

Kriterii Ioffe-Regelya i diffuziya kolebanii v neuporyadochennykh sistemakh

27 September 2012 in 11:30

Ya.M. Bel’tyukov, D.A. Parshin, V.I. Kozub (Sankt-Peterburg)

S pomoshch’yu teorii sluchainykh matrits issledovana diffuziya kolebanii v sluchainykh reshetkakh, obladayushchikh translyatsionnoi invariantnost’yu. Pokazano, chto vyshe opredelennoi chastoty ωIR, sootvetstvuyushchei kriteriyu Ioffe-Regelya, ponyatie fononov teryaet svoi smysl. Oni ne mogut rasprostranyat’sya po reshetke i perenosit’ kvaziimpul’s i energiyu. Tem ne menee, v otlichie ot lokalizatsii elektronov, bol’shinstvo kolebanii v etoi oblasti chastot ne yavlyayutsya lokalizovannymi. Oni rasprostranyayutsya v reshetke diffuzionnym obrazom i poetomu poluchili nazvanie diffuzonov. Pokazano, chto diffuzony dominiruyut v spektre kolebanii stekol i opredelyayut temperaturnuyu zavisimost’ teploprovodnosti v oblasti temperatur, kotoraya v tipichnykh steklakh zanimaet podavlyayushchuyu chast’ eksperimental’no dostupnoi temperaturnoi shkaly. Fonony, naprotiv, sostavlyayut v spektre kolebanii stekol vsego lish’ ot 0.2% do 4% ot vsekh kolebatel’nykh mod. Menyaya stepen’ besporyadka, my mozhem menyat’ chastotu ωIR ot nulya (kogda zhestkost’ reshetki ravna nulyu i v nei voobshche otsutstvuyut fonony), do predel’nykh fononnykh chastot kristalla. Kak izvestno, chislo diffundiruyushchikh velichin v neuporyadochennoi sisteme opredelyaetsya chislom integralov dvizheniya. My vychislili koeffitsient diffuzii energii D(ω) i koeffitsient diffuzii impul’sa Du, kotorye, kak okazalos’, chislenno razlichayutsya. Dinamicheskii strukturnyi faktor S(q,ω) vyshe chastoty ωIR sovpadaet so strukturnym faktorom sluchainykh bluzhdanii chastits po reshetke, i v nashem sluchae kharakterizuet sluchainye bluzhdaniya smeshchenii ot atoma k atomu. Koeffitsient diffuzii impul’sa (vyazkost’) Du — opredelyaet shirinu kolebatel’nogo spektra Γ(q) = Duq2 v etoi oblasti chastot, chto ob’yasnyaet eksperimenty po neuprugomu rentgenovskomu rasseyaniyu v steklakh, provodivshiesya poslednie 15 let.

Superinductors: a novel type of Josephson ladders implementing quantum Ising model

20 September 2012 in 11:30

Lev Ioffe (Rutgers University & Universite Paris VI)

Implementation of superinductor, the element that is characterized by a purely inductive response and impedance much larger than quantum (6.5 kOhm), is a very long standing challenge. Recently, we have designed and implemented it in very special Josephson ladders with tunable frustration. The same ladders allows one an experimental realization of the one dimensional φ4 theory with the mass that changes sign with magnetic field. Close to the critical point the low energy excitations in this theory can be described by Ising model in transverse field. The solution of the latter shows that these excitations are Majorana fermions. Can these fermionic excitations be observed in Josephson ladders?

Surprises, Computational Methods, and Results for Metastable Phenomena and Homogeneous Nucleation and Growth

5 July 2012 in 11:30

Mark Novotny (Mississippi State University)

It is shown that even in the simplest models homogeneous nucleation and growth is complicated, leading to a “phase diagram” that depends on the various length scales in the problem. Algorithms that allow faster-than-real-time simulations to span the disparate timescales in nucleation will be presented. Specific results discussed will include the dependence of the hysteresis loop on the frequency, whether changing the dynamics can change the exponent in the nucleation rate, and a Dynamic Phase Transition (including experimental confirmation in magnetic multilayer systems).

Hanbury Brown and Twiss setup with anyons

24 May 2012 in 11:30

Gabriele Campagnano, Oded Zilberberg, Igor V. Gornyi, Dmitri E. Feldman, Andrew C. Potter, Yuval Gefen

We present a study of an Hanbury Brown and Twiss (HBT) interferometer realized with anyons. Such a device can directly probe entanglement and fractional statistics of initially uncorrelated particles. We calculate HBT cross-correlations of Abelian Laughlin anyons. The correlations we calculate exhibit partial bunching similar to bosons, indicating a substantial statistical transmutation from the underlying electronic degrees of freedom. We also find qualitative differences between the anyonic signal and the corresponding bosonic or fermionic signals, indicating that anyons cannot be simply thought as intermediate between bosons and fermions.

Enhancement of the retrapping current of superconducting microbridges of finite length

17 May 2012 in 11:30

Denis Vodolazov (Institute for Physics of Microstructures RAS, Nizhny Novgorod)

V rabote teoreticheski issledovano vliyanie velichiny parametra poryadka v sverkhprovodyashchikh beregakh |Δ|lead na protsess proskal’zyvaniya fazy i vol’t-ampernye kharakteristiki sverkhprovodyashchikh nanoprovolok/mikromostikov konechnoi dliny. Bylo obnaruzheno, chto nebol’shoe podavlenie |Δ|lead privodit k umen’sheniyu soprotivleniya mikromostika i uvelicheniyu toka vozvrata (retrapping current) sverkhprovodnika v sverkhprovodyashchee sostoyanie. Obnaruzhennyi effekt svyazan s uvelicheniem potoka «goryachikh» neravnovesnykh kvazichastits (indutsirovannykh ostsillyatsiyami |Δ| v tsentre mostika) v berega pri umen’shenii |Δ|lead. Poluchennyi rezul’tat mozhet byt’ ispol’zovan pri ob’yasnenii otritsatel’nogo magnetosoprotivleniya, eksperimental’no obnaruzhennogo v neskol’kikh nedavnikh eksperimentakh na sverkhprovodyashchikh nanoprovolokakh/mikromostikakh.

Double proximity effect in hybrid planar Superconductor-(Normal metal/Ferromagnet)-Superconductor structures

26 April 2012 in 11:30

V.V. Ryazanov (ISSP RAS)

We have investigated the differential resistance of hybrid planar Al-(Cu/Fe)-Al submicron bridges at low temperatures and in weak magnetic fields. The structure consists of Cu/Fe-bilayer forming a bridge between two superconducting Al-electrodes. In superconducting state of Al-electrodes, we have observed a double-peak peculiarity in differential resistance of the S-(N/F)-S structures at a bias voltage corresponding to the minigap. We claim that this effect (the doubling of the minigap) is due to an electron spin polarization in the normal metal which is induced by the ferromagnet. We have demonstrated that the double-peak peculiarity is converted to a single peak at a coercive applied field corresponding to zero magnetization of the Fe-layer.

Vortex dynamics in Fermi superfluids at ultra low temperatures

12 April 2012 in 11:30

Mihail Silaev (Institute for Physics of Microstructures RAS, Nizhny Novgorod)

We show that the vortex dynamics in Fermi superfluids at ultra-low temperatures is governed by the local heating of the vortex cores creating the heat flux carried by non-equilibrium quasiparticles emitted by moving vortices. This mechanism provides a universal zero temperature limit of dissipation in Fermi superfluids. For the typical experimental conditions realized by the turbulent motion of 3He-B the temperature of vortex cores is estimated to be of the order 0.2 Тс. The dispersion of Kelvin waves is derived and the heat flow generated by Kelvin cascade is shown to have the value close to the experimentally observed. The suggested mechanism can provide the low-temperature limit of dissipation for mechanical pendulum such as vibrating wire resonator in 3He-B.

Vliyanie kvazichastichnoi inzhektsii na zavisyashchii ot chastoty otklik sverkhprovodnika

5 April 2012 in 11:30

K.E. Nagaev (IRE RAN)

Vychislen lineinyi otklik neravnovesnogo provodnika na peremennoe elektricheskoe pole. Neravnovesnost’ v nem sozdaetsya putem inzhektsii kvazichastits iz normal’nykh elektrodov cherez tunnel’nye kontakty s neodinakovoi prozrachnost’yu. Dissipativnaya chast’ otklika proportsional’na summarnoi plotnosti inzhektirovannykh kvazichastits nezavisimo ot sootnosheniya chisel dyrochno-podobnykh i elektrono-podobnykh vozbuzhdenii. Pri fiksirovannoi plotnosti kvazichastits dissipatsiya uvelichivaetsya s ponizheniem temperatury.

Mnogochastichnye sostoyaniya v otkrytykh kvantovykh sistemakh. Maioranovskie fermiony.

29 March 2012 in 11:30

Mikhail Baranov (Innsbruck, Austria)

Obsuzhdaetsya sposob sozdaniya korrelirovannykh mnogochastichnykh sostoyanii v otkrytykh kvantovykh sistemakh (kvantovykh sistemakh, opredelennym obrazom vzaimodeistvuyushchikh s rezervuarom). Osnovnoe vnimanie udelyaetsya odnomernoi atomnoi tsepochke s maioranovskimi kraevymi sostoyaniyami i svyazi poslednikh s netrivial’noi topologiei matritsy plotnosti sistemy.

Solution of the Dyson-Schwinger equation on de Sitter background in IR limit

22 March 2012 in 11:30

Emil Akhmedov (ITEP)

We propose an ansatz which solves the Dyson-Schwinger equation for the real scalar fields in Poincare patch of de Sitter space. In the IR limit the Dyson-Schwinger equation for this ansatz reduces to the kinetic equation, if one considers scalar fields from the principle series. Solving the latter equation we show that under the adiabatic switching on and then off the coupling constant the Bunch-Davies vacuum relaxes to the state with the flat Gibbons-Hawking density of out-Jost harmonics on top of the corresponding de Sitter invariant out-vacuum.

Kvantovye fluktuatsii v kvaziodnomernykh sverkhprovodnikakh

1 March 2012 in 11:30

K.Yu. Arutyunov (University of Jyväskylä, Finland & SINP MSU)

V poslednee vremya vopros kvantovykh fluktuatsii v kvaziodnomernykh sverkhprovodnikakh, takzhe eshche chasto nazyvaemykh kvantovym proskal’zyvaniem fazy (KPF), stal privlekat’ interes nauchnoi obshchestvennosti [1]. V chastnosti bylo obnaruzheno, chto effekt privodit k konechnomu soprotivleniyu tonkikh «sverkhprovodyashchikh» nanoprovodov pri temperaturakh sushchestvenno nizhe kriticheskoi TTc [2-6]. Sovsem nedavno bylo eksperimental’no prodemonstrirovano, chto tot zhe samyi effekt — kvantovoe proskal’zyvanie fazy — privodit k podavleniyu nezatukhayushchikh diamagnitnykh tokov v ochen’ tonkikh kolechkakh [7], privodya k otkrytiyu energeticheskoi shcheli v spektre, kotoroe mozhet byt’ ispol’zovano dlya postroeniya kvantovoi dvukhurovnevoi sistemy [8]. Teoreticheski bylo pokazano, chto tonkii sverkhprovodyashchii kanal v rezhime kvantovykh fluktuatsii dualen Dzhozefsonovskomu kontaktu [9]. Predskazanie vedet k dostatochno neozhidannomu rezul’tatu: sverkhprovodnik dolzhen demonstrirovat’ izoliruyushchee sostoyanie — Kulonovskuyu blokadu. Sovsem nedavno avtorom byl prodemonstrirovan etot effekt v sverkhtonkikh titanovykh nanoprovodakh. Bolee togo, analogiya s Dzhozefsonovskoi sistemoi predpolagaet, chto esli smeshchennyi po toku kvaziodnomernyi sverkhprovodnik obluchaetsya vneshnim VCh izlucheniem s chastotoi f, to na VAKh dolzhny nablyudat’sya spetsificheskie osobennosti — Blokhovskie stupen’ki — pri kvantovannykh znacheniyakh toka In=n×(2ef, gde n — tseloe chislo i 2e — zaryad Kuperovskoi pary. V tekh zhe samykh titanovykh nanoprovodakh eti Blokhovskie osobennosti byli takzhe prodemonstrirovany. Ozhidaetsya, chto v polnoi analogii s effektom Shapiro v Dzhozefsonovskikh kontaktakh, etot effekt mozhet privesti k vazhnomu metrologicheskomu primeneniyu — kvantovomu etalonu toka. [1] K. Yu. Arutyunov, D.S. Golubev, and A.D. Zaikin, Phys. Rep. 464, 1 (2008). [2] N. Giordano, Phys. Rev. Lett. 61, 2137 (1988). [3] A. Bezryadin, C.N. Lau, and M. Tinkham, Nature 404, 971 (2000). [4] M. Zgirski, K.-P. Riikonen, V. Touboltsev, and K. Arutyunov, NanoLett. 5, 1029 (2005). [5] M. Zgirski, K.-P. Riikonen, V. Touboltsev, and K.Yu. Arutyunov, Phys. Rev. B 77, 054508 (2008). [6] J.S. Lehtinen, T. Sajavaara, K.Yu. Arutyunov, and A. Vasiliev, arXiv:1106.3852v1 (2011). [7] K.Yu. Arutyunov, T.T. Hongisto, J.S. Lehtinen, L.I. Leino, and A.S. Vasiliev, Nature: Sci. Rep. 2(293), 1 (2012). [8] O.V. Astafiev, L.B. Ioffe, S. Kafanov, Yu.A. Pashkin, K.Yu. Arutyunov, D. Shahar, O. Cohen, and J.S. Tsai, Nature 482, to be published (March, 2012). [9] J.E. Mooij and Yu.V. Nazarov, Nature Physics 2, 169 (2006).

Counting free fermions on a line: a Fisher-Hartwig asymptotic expansion for the Toeplitz determinant in the double-scaling limit

19 January 2012 in 11:30

Dmitri Ivanov (ETH Zurich and Univeristy of Zurich), Alexander Abanov, Vadim Cheianov

We derive an asymptotic expansion for a Fredholm determinant arising in the problem of counting one-dimensional free fermions on a line segment at zero temperature. This asymptotic expansion was conjectured previously from numerical evidence. It is explicitly periodic in the «counting parameter» and describes the nonanalytic dependence of the asymptotic behavior of the determinant on this parameter. The derived expansion is an extension of the result in the theory of Toeplitz determinants known as the generalized Fisher-Hartwig conjecture. We present two ways to derive our result: the matrix Riemann-Hilbert problem and the Painleve V equation. We prove that the expansion coefficients are polynomials in the counting parameter, provide an algorithm for their calculation order by order and list explicitly first several coefficients. (arXiv:1112.2530)

Multifractality of wave functions: basic concepts and experiment

29 December 2011 in 11:30

Vladimir Kravtsov (ICTP, Trieste, Italy)

Wave functions in certain disordered systems exhibit a special scaling called «multifractality». Discovered in the 80-th as the property of critical states near the Anderson transition point, this phenomenon has been rapidly developing recently with new important results about the scaling relationships between the fractal dimensions and the origin of these relationships in CFT. At the same time, the critical states near the Anderson transition become accessible experimentally in cold atom systems, in disordered 2D electron gases in semiconductors and in sound wave propagation in strongly disordered media. I will review these new results and some recent theoretical predictions.

Heat, work and fluctuation relations in single-electron transport: experimental test of the Jarzynski equality

22 December 2011 in 11:30

Jukka Pekola (Aalto University, Finland )

The physical foundations of commonplace concepts such as information, work and heat can be studied in detail in small systems having just few degrees of freedom. Characteristic of such systems is that the magnitude of thermal fluctuations of energy and coordinate variables can be significant compared to their mean behavior. Fluctuation relations have been developed relatively recently to describe these phenomena. They have been successfully applied in the interpretation of, e.g., experiments performed on individual complex biomolecules. However, a «textbook» example of nontrivial nonequilibrium thermal fluctuations measured in a well-characterized system has been missing. Here we demonstrate experimental readout of the distribution of dissipated energy in a metallic single-electron box that we subject to an external nonadiabatic gate drive at sub-kelvin temperatures [1]. In contrast to previous experimental work, the total heat dissipated in an electron tunneling event can be directly determined from the timing of the tunneling event with respect to the external drive [2]. Also, being a lithographically defined electronic system, the experimental gate protocol can be repeated accurately and indefinitely without degrading the sample, allowing us to recover the heat distribution with a dynamic range of more than three orders of magnitude. The present work shows that nonequilibrium thermodynamics can be studied in solid state systems where realization of quantum coherence effects and an engineered non-Gaussian environment is experimentally feasible. [1] O.-P. Saira et al., in preparation. [2] D.V. Averin and J.P. Pekola, EPL 96, 67004 (2011).

Zakon vozrastaniya entropii s tochki zreniya kvantovoi mekhaniki

15 December 2011 in 11:30

G.B. Lesovik

Vtoroi zakon termodinamiki, odin iz fundamental’nykh zakonov prirody, na segodnyashnii den’ po-prezhnemu predstavlyaetsya ne do kontsa ponyatnym i vyzyvayushchim voprosy. Imenno tak on predstavlen i v uchebnikakh — naprimer v «Statisticheskoi fizike» Landau i Lifshitsa. Vmeste s tem, razvitie kvantovoi mekhaniki i kvantovoi informatiki poslednikh let pozvolyaet ponyat’ proiskhozhdenie vtorogo zakona i svyazannoi s nim kontseptsii neobratimosti (vyrazhayushcheisya v vozrastanii entropii so vremenem), po krainei mere, na kachestvennom urovne. Imenno kachestvennomu rassmotreniyu budet posvyashchena bol’shaya chast’ doklada. Krome togo, my obsudim nekotorye aspekty kolichestvennogo opisaniya. V chastnosti, budut rassmotreny: 1) Rost entropii v rezul’tate kvantovoi zaputannosti sistemy i rezervuara na primere chastitsy, bluzhdayushchei po reshetke s detektorami na rebrakh reshyotki, i v zadache o statistike perenosa zaryada v kvantovom provodnike. 2) Usloviya obratimosti evolyutsii sistemy. Narushenie simmetrii v gil’bertovom prostranstve sostoyanii.

Tunneling electro-conductance of Bose condensates

8 December 2011 in 11:30

Vladimir Akulin (Orsay, France)

Interaction of an electron with a Bose condensate of atoms having electron affinity is considered. States of an electron trapped by such atoms form a continuous band, although tunneling through this band is strongly suppressed by quantum fluctuations of the condensate density. Still the transport process turns to be possible when inelastic processes associated with quantum transitions in the condensate are taken into account. One can adapt the standard field theory methods that originally have been developed for description of a particle propagating trough a disordered potential and present an exactly soluble analytical model of the process.

Fototoki v grafene i topologicheskikh izolyatorakh

1 December 2011 in 11:30

L.E. Golub (FTI im. A.F. Ioffe RAN)

Opticheskoe vozbuzhdenie grafena polyarizovannym svetom privodit k chisto dolinnomu toku, pri kotorom nositeli v dolinakh tekut v protivopolozhnye storony. Tok v kazhdoi doline generiruetsya blagodarya asimmetrii opticheskikh perekhodov i rasseyaniya elektronov na primesyakh, obuslovlennoi gofrirovkoi elektronnogo energeticheskogo spektra. Napravlenie dolinnogo toka opredelyaetsya orientatsiei ploskosti polyarizatsii sveta otnositel’no kristallograficheskikh osei. Elektron-elektronnoe rasseyanie privodit k dopolnitel’nomu vkladu v dolinnyi tok, kotoryi yavlyaetsya dominiruyushchim v nelegirovannom grafene na podlozhke s vysokoi dielektricheskoi pronitsaemost’yu. Obsuzhdayutsya vozmozhnosti elektricheskogo i opticheskogo detektirovaniya dolinnykh fototokov. Takzhe rassmotreny sverkhreshyotki, sformirovannye periodicheskoi deformatsiei lista grafena. Pokazano, chto asimmetrichno deformirovannyi grafen deistvuet kak kvantovyi khrapovik (ratchet), generiruya elektricheskii tok pri pogloshchenii normal’no padayushchego sveta. Fototok, chuvstvitel’nyi k znaku tsirkulyarnoi polyarizatsii, rasschitan dlya sverkhreshyotok s razlichnoi stepen’yu asimmetrii. Pomimo grafena, v rabote izucheny fotogal’vanicheskie effekty v kvantovykh yamakh s invertirovannoi zonnoi strukturoi, gde realizuetsya odnomernyi topologicheskii izolyator. Pokazano, chto pri osveshchenii takoi sistemy ellipticheski polyarizovannym svetom s energiei kvanta, men’shei shiriny zapreshchennoi zony, voznikayut kraevye fototoki. Toki na protivopolozhnykh krayakh obraztsa napravleny v protivopolozhnye storony i menyayut polyarnost’ pri izmenenii znaka krugovoi polyarizatsii vozbuzhdayushchego izlucheniya.

Spin-zavisimaya opticheskaya spektroskopiya nanostruktur

17 November 2011 in 11:30

E.L. Ivchenko (Fiziko-tekhnicheskii institut im. A.F. Ioffe RAN, S.-Peterburg)

V vvodnoi chasti doklada budet dan obzor spin-zavisimykh yavlenii, izuchaemykh v nashei teoreticheskoi gruppe FTI dlya razvitiya metodov generatsii, nakopleniya i detektirovaniya elektronnoi spinovoi polyarizatsii, a takzhe upravleniya eyu. Zatem ya pereidu k bolee podrobnomu rassmotreniyu spektroskopii zaryazhennykh i neitral’nykh kvantovykh tochek. (1) Spinovaya dinamika elektronov v zaryazhennykh kvantovykh tochkakh. V nastoyashchee vremya v opticheskoi spektroskopii dlya izucheniya spinovoi orientatsii elektronov v nanostrukturakh shiroko primenyaetsya dvukhpuchkovyi metod «nakachka-zondirovanie» (pump-probe), po-vidimomu, vpervye predlozhennyi dlya ob’emnykh poluprovodnikov v teoreticheskoi rabote [1]. Budut rassmotreny yavleniya, svyazannye s opticheskim upravleniem elektronymi spinami i sinkhronizatsiei mod spinovoi pretsessii elektronov v massivakh kvantovykh tochek n-tipa pri ikh nakachke periodicheskoi posledovatel’nost’yu opticheskikh impul’sov [2]. (2) Tonkaya struktura eksitonov v neitral’nykh kvantovykh tochkakh. Budet predstavlena teoriya obmennogo elektron-dyrochnogo vzaimodeistviya v nanostrukturakh i proanalizirovano, kak zavisit kharakter rasshchepleniya eksitonnykh podurovnei ot formy nanostrukturnogo potentsiala i orientatsii kvantovoi tochki otnositel’no kristallograficheskikh osei. V etoi chasti ya rasskazhu o novykh rezul’tatakh [3] eksperimental’nogo i teoreticheskogo izucheniya spinovykh svoistv nenapryazhennykh kvantovykh tochek GaAs/AlGaAs(111). [1] A.G. Aronov, E.L. Ivchenko, FTP 15, 231 (1973). [2] I.A. Yugova, M. M. Glazov, E.L. Ivchenko, Al. L. Efros, Phys. Rev. B 80, 104436 (2009); L.V. Fokina, I.A. Yugova, D.R. Yakovlev, M.M. Glazov, I.A. Akimov et al., Phys. Rev. B 81, 195304 (2010). [3] G. Sallen, B. Urbaszek, M. M. Glazov, E. L. Ivchenko, T. Kuroda et al., Phys. Rev. Lett. 107, 166604 (2011).

Topologicheskie invarianty i nulevye fermionnye mody v gelii-3 V i topologicheskikh sverkhprovodnikakh

3 November 2011 in 11:30

Mihail Silaev (Institute for Physics of Microstructures RAS, Nizhny Novgorod)

Odnoi iz populyarnykh tematik v sovremennoi fizike kondensirovannykh sred yavlyaetsya izuchenie svoistv sistem so shchel’yu v fermionnom spektre kvazichastits, v to zhe vremya obladayushchikh netrivial’noi topologiei grinovskikh funktsii. K chislu takikh sistem otnosyatsya topologicheskie izolyatory, a takzhe sverkhtekuchii gelii-3 V i topologicheskie sverkhprovodniki. V doklade budut rassmotreny nekotorye iz takikh soedinenii. Takzhe budut privedeny primery primeneniya teoremy ob indeksakh, opredelyayushchei chislo nulevykh mod na granitsakh, domennykh stenkakh i v korakh vikhrei v sverkhtekuchem gelii-3 V i topologicheskikh sverkhprovodnikakh.

Kvantovaya Optika s odnofotonnymi istochnikami

20 October 2011 in 11:30

Aleksei Akimov (FIAN)

Sushchestvennaya chast’ doklada budet posvyashchena ispol’zovaniyu plazmonnykh nanoprovolok dlya raboty s odnofotonnymi istochnikami, ot effektivnogo sbora fotonov s tverdotel’nykh odnofotonnykh istochnikov do uderzhaniya odinochnykh atomov v oblastyakh nanometrovogo razmera. Takzhe budut korotko obsuzhdeny tsentry okraski v almaze ne tol’ko kak istochniki odinochnykh fotonov, no i vozmozhnyi kandidat na osnovnoi element kvantovogo protsessora ili sensora nanometrovogo razresheniya.

Majorana fermions in pinned vortices

13 October 2011 in 11:30

Alexander Rozhkov (Institute for Theoretical and Applied Electromagnetics, RAS)

Exploiting the peculiar properties of proximity-induced superconductivity on the surface of a topological insulator, we propose a device which allows the creation of a Majorana fermion inside the core of a pinned Abrikosov vortex. The relevant Bogolyubov-de Gennes equations are studied analytically. We demonstrate that in this system the zero-energy Majorana fermion state is separated by a large energy gap, of the order of the zero-temperature superconducting gap Δ, from a band of single-particle non-topological excitations. In other words, the Majorana fermion remains robust against thermal fluctuations, as long as the temperature remains substantially lower than the critical superconducting temperature. Experimentally, the Majorana state may be detected by measuring the tunneling differential conductance at the center of the Abrikosov vortex. In such an experiment, the Majorana state manifests itself as a zero-bias anomaly separated by a gap, of the order of Δ, from the contributions of the nontopological excitations. [A.L. Rakhmanov, A.V. Rozhkov, Franco Nori, Phys. Rev. B 84, 075141 (2011)]

Universal manifestations of electron-electron interaction in conductivity of a 2D metal near a convex-concave Fermi surface transition

6 October 2011 in 11:30

Vladimir Yudson (Institute for Spectroscopy RAS, Troitsk)

In the absence of umklapp scattering, the existence of the Fermi-liquid (T2) term in conductivity of a 2D metal depends on the Fermi surface geometry, in particular, on whether it is convex or concave. Due to hexagonal warping, the Fermi surface of 2D metallic surface states of 3D topological insulators of the Bi2Te3 family changes its shape (from convex to concave) on doping, while still being too small to allow for umklapp scattering. We show that near a convex-concave transition the T2 term in the conductivity obeys a universal scaling form. [H.K. Pal, V.I. Yudson, D.L. Maslov, arXiv:1108.2435]

Nestatsionarnyi rezhim elektronnogo transporta cherez primes’ v odnomernoi sisteme s sil’nym mezhelektronnym ottalkivaniem

29 September 2011 in 11:30

D.S. Shapiro, S.N. Artemenko (IRE RAN)

Issleduetsya provodimost’ 1D sistemy vzaimodeistvuyushchikh elektronov s primes’yu. Mezhelektronnoe ottalkivanie opisyvaetsya v ramkakh bozonizovannogo gamil’toniana Tomonagi-Lattindzhera. Rassmotreny sluchai korotkodeistvuyushchego vzaimodeistviya (voznikayushchego v kvantovykh provolokakh za schet ekranirovaniya zatvorom) i dal’nodeistvuyushchego kulonovskogo vzaimodeistviya. Poluchennye uravneniya dvizheniya dlya gaizenbergovskogo operatora bozonnogo polya smeshcheniya v tochke primesi imeyut vid uravnenii kolebanii mayatnika. Eti uravneniya strogo resheny v kvaziklassicheskom predele, sootvetstvuyushchem sil’nomu mezhelektronnomu ottalkivaniyu, kogda fluktuatsii v zaryadovom kanale maly. Pri etom dlya sluchaya elektronov so spinom reshenie dlya spinovogo kanala, v kotorom fluktuatsii nel’zya schitat’ malymi, udaetsya naiti s pomoshch’yu metoda refermionizatsii, primenimogo v sluchae vzaimodeistviya, ne zavisyashchego ot spina. Tak kak uravneniya pokhozhi na uravnenie dvizheniya mayatnika, reshenie daet postoyannyi i peremennyi toki, chastota peremennogo toka opredelyaetsya velichinoi postoyannogo toka, f = I/e. Reshenie, opisyvayushchee kolebaniya, polucheno takzhe v samosoglasovannom garmonicheskom priblizhenii (gaussova model’ fluktuatsii). V sluchae korotkodeistviya eto priblizhenie obosnovyvaetsya v predele bol’shikh napryazhenii i pri dostatochno sil’nom ottalkivanii (lattindzherovskii parametr vzaimodeistviya Kρ < 1/2), kogda vysshie kumulyanty ubyvayut s rostom napryazheniya, tak chto fluktuatsii mozhno schitat’ blizkimi k gaussovym. Pri kulonovskom dal’nodeistvii effekt mozhno strogo obosnovat’ i pri umerennoi velichine ottalkivaniya, kogda parametr e2/(ℏvF) ∼ 1. Eto svyazano s logarifmicheskoi raskhodimost’yu fur’e-obraza kulonovskogo potentsiala v dlinnovolnovom predele, chto privodit k bolee effektivnomu obrezaniyu infrakrasnoi raskhodimosti, kharakternoi dlya 1D sistem. V sluchae kulonovskogo vzaimodeistviya effekt mozhno rassmatrivat’ kak skol’zhenie «odnomernogo vignerovskogo kristalla» v usloviyakh pinninga na primesi.

Renormgruppovye issledovaniya dvumernykh fermi-sistem

22 September 2011 in 11:30

Andrey Katanin (Institute of Metal Physics, Ekaterinburg)

V doklade rassmatrivaetsya primenenie metoda funktsional’noi renormgruppy k opisaniyu dvumernykh fermionnykh sistem. Dlya nesingulyarnoi plotnosti sostoyanii privodyatsya strogie rezul’taty dokazatel’stva fermi-zhidkostnogo povedeniya vo vsekh poryadkakh teorii vozmushchenii. Fizicheski interesnyi sluchai singulyarnostei van Khova v elektronnom spektre proanalizirovan chislenno v odno- i dvukhpetlevom priblizhenii, chto pozvolyaet opredelit’ temperaturnye zavisimosti vospriimchivostei, simmetriyu magnitnogo i sverkhprovodyashchego parametrov poryadka i predpolagaemye fazovye diagrammy osnovnogo sostoyaniya vblizi ferro- i antiferromagnitnykh neustoichivostei. Analiziruyutsya vozmozhnye stsenarii narusheniya fermi-zhidkostnogo povedeniya vblizi magnitnykh i sverkhprovodyashchikh neustoichivostei, a takzhe perspektivy razvitiya metoda funktsional’noi renormgruppy.

Dvumernye dirakovskie fermiony i topologicheskii izolyator v kvantovykh yamakh na osnove HgTe

1 September 2011 in 11:30

Z.D. Kvon (Institute of Semiconductor Physics, Novosibirsk)

Izlagayutsya rezul’taty eksperimental’nogo issledovaniya bezmassovykh odnodolinnykh dvumernykh (2D) dirakovskikh fermionov (DF), a takzhe 2D razuporyadochennogo topologicheskogo izolyatora (TI) v kvantovykh yamakh na osnove HgTe kvantovykh yam. Dvumernye DF nablyudayutsya v yamakh tolshchinoi d = 6.6 nm, sootvetstvuyushchei perekhodu ot pryamogo k invertirovannomu spektru. Oni imeet printsipial’noe otlichie ot DF v grafene, tak kak lineinyi spektr v HgTe kvantovannykh yamakh vyzvan relyativistkoi prirodoi energeticheskogo spektra HgTe, a ne osobym raspolozheniem atomov. Po etoi prichine v ikh povedenii velika rol’ spin-orbital’nogo vzaimodeistviya i zeemanovskogo rasshchepleniya. Takzhe nemalovazhen tot fakt, chto podvizhnost’ DF v HgTe yamakh dostigaet velichiny 2∙105 sm2/Vs, togda kak v grafene ona na poryadok men’she. Izmereny transportnyi i emkostnyi otklik sistemy. On pokazyvaet, chto spektr v zone provodimosti yavlyaetsya lineinym pri vsekh dostizhimykh energiyakh. Valentnaya zona ustroena slozhnee, i naryadu s bezmassovymi dirakovskimi dyrkami pri energiyakh na 10 meV nizhe dirakovskoi tochki voznikaet zona tyazhelykh dyrok s ekstremumami vne tsentra zony Brillyuena. Ustanovleno, chto pri nizkikh temperaturakh (T < 0.2 K) vblizi dirakovskoi tochki provodimost’ sistemy σ > 1.5 e2/h i opredelyaetsya effektami vzaimodeistviya i slaboi antilokalizatsii, ukazyvayushchei na bystruyu spinovuyu relaksatsiyu DF. Obnaruzheno rasseyanie bezmassovykh DF massivnymi dyrkami. V zaklyuchenie obsuzhdayutsya osobennosti kvantovogo effekta Kholla. 2D topologicheskii izolyator realizovan v HgTe kvantovykh yamakh, imeyushchikh tolshchinu d = 8 nm - 9 nm. Izmereniyami nelokal’nogo soprotivleniya pokazano, chto odnomernaya provoloka, realizuemaya v takom dvumernom TI vdol’ kraev kvantovoi yamy, mozhet dostigat’ dlin neskol’ko millimetrov. Ee kondaktans g ~ 0.1. Naideno, chto dazhe v takoi dlinnoi provoloke otsutstvuyut effekty lokalizatsii, vidimo, blagodarya topologicheskoi ustoichivosti issledovannogo 2D TI. Obnaruzhen proboi TI prodol’nym magnitnym polem.

Coulomb drag between quantum wires

23 June 2011 in 11:30

A.P. Dmitriev, I.V. Gornyi, D.G. Polyakov (Karlsruhe Institute of Technology, Germany)

We revisit the problem of Coulomb drag between ballistic one-dimensional electron systems. Within the Boltzmann kinetic approach, we demonstrate that the equilibration between the right- and left-movers in the wires is crucially important for establishing dc drag. This relaxation requires either interwire electron-electron backscattering or processes involving the scattering of electrons near the bottom of the spectrum. The forward pairwise scattering of electrons near the Fermi level is therefore not sufficient, in contrast to a number of works studying drag due to this mechanism of scattering, for nonzero dc drag resistivity. At sufficiently high temperatures, the «left-right» relaxation (and hence the drag effect) is dominated by the triple inelastic collisions involving a «cold» electron near the band bottom. This yields the activation temperature dependence of the transresistivity, which we calculate from the Fokker-Planck equation.

Theory of fractional quantum Hall interferometers

16 June 2011 in 11:30

E. Sukhorukov (University of Geneva)

Interference of fractionally charged quasi-particles is expected to lead to Aharonov-Bohm oscillations with periods larger than the flux quantum. However, according to the Byers-Yang theorem, observables of an electronic system are invariant under adiabatic insertion of a quantum of singular flux. We resolve this seeming paradox by considering a microscopic model of an electronic interferometer made from a quantum Hall liquid at filling factor 1/m in the shape of a Corbino disk. Quantum Hall edge states are utilized in place of optical beams, quantum point contacts play the role of beam splitters connecting different edge channels, and Ohmic contacts may be considered a source and drain of a quasi-particle current. Depending on the position of Ohmic contacts one distinguishes interferometers of Fabry-Perot (FP) and Mach-Zehnder (MZ) type. An approximate ground state of such interferometers is described by a Laughlin type wave function, and low-energy excitations are incompressible deformations of this state. We construct a low-energy effective theory by projecting the state space of the liquid onto the space of incompressible deformations and show that the theory of the quantum Hall edge so obtained is a generalization of a chiral conformal field theory. A quasi-particle tunneling operator in our theory is found to be a single-valued function of tunneling point coordinates, and its phase depends on the topology, determined by the positions of Ohmic contacts. We describe strong coupling of the edge states to Ohmic contacts and the resulting quasi-particle current through the interferometer with the help of a master equation. We find that the coherent contribution to the average quasi-particle current through MZ interferometers vanishes after the summation over quasi-particle degrees of freedom. Remaining contribution originates from electron tunneling and oscillates with the electronic period, in agreement with the Byers-Yang theorem. When a magnetic flux through FP interferometers is varied with a modulation gate, current oscillations have the quasi-particle periodicity, thus allowing for the spectroscopy of quantum Hall edge states. Importantly, in contrast to previous models our theory does not rely on any ad-hoc constructions, such as Klein factors.

Perekhod sverkhprovodnik-izolyator i lokalizatsiya energii (prodolzhenie)

9 June 2011 in 11:30

M.V. Feigel'man

Perekhod sverkhprovodnik-izolyator i lokalizatsiya energii

26 May 2011 in 11:30

M.V. Feigel'man

Budet dan obzor imeyushcheisya (v zachatochnoi forme) teorii sil’no neuporyadochennykh sverkhprovodnikov s psevdoshchel’yu, i kvantovogo fazovogo perekhoda iz etogo sostoyaniya v sostoyanie izolyatora. Posle etogo predpolagaetsya predstavit’ i obsudit’ dlinnyi ryad otkrytykh voprosov, kak teoreticheskikh, tak i eksperimental’nykh.

Electronic transport through a contact of a correlated quantum wire with leads of higher dimension

19 May 2011 in 11:30

S.N. Artemenko, P.P. Aseev, D.S. Shapiro (IRE RAS)

We study theoretically electronic transport through a contact of a quantum wire with 2D or 3D leads. Usually, the boundary conditions derived by Egger and Grabert for ideal adiabatic contacts are used to describe electronic transport in such systems. But these conditions were derived only for expectation values and, therefore, they do not take into account fluctuations, which are very important in 1D systems, and do not describe relaxation processes in 1D conductor due to coupling to bulk electrodes playing a role of the heat bath. Further, the real contacts are not necessarily adiabatic, and this may result in formation of Friedel oscillations (FO) near the contacts. We derive boundary conditions for non-adiabatic contacts taking into account fluctuations and find that if the contact is not smooth and adiabatic then the FO are really formed and suppress conduction in 1D system with inter-electronic repulsion. We apply the derived boundary conditions to study dynamic regime of conduction related to formation of FO near the contacts.

Diffuziya Arnol’da v diskretnom nelineinom uravnenii Shryodingera s sil’nym besporyadkom

28 April 2011 in 11:30

D. Basko (CNRS, Grenoble, France)

Izuchaetsya vopros o nalichii i kharaktere transporta v klassicheskoi gamil’tonovoi sisteme so slaboi nelineinost’yu, v situatsii kogda normal’nye mody lineinoi zadachi sil’no lokalizovany po Andersonu. Statisticheskii analiz prostranstvennoi struktury khaoticheskogo dvizheniya v sisteme pozvolyaet vyvesti makroskopicheskie uravneniya dlya transporta sokhranyayushchikhsya velichin (normy i energii), i poluchit’ yavnye vyrazheniya dlya transportnykh koeffitsientov. (arXiv:1005.5033)

Optical excitation of Electron-Glasses

21 April 2011 in 11:30

Z. Ovadyahu (Racah Institute of Physics, The Hebrew University, Jerusalem)

Electron-glasses can be readily driven far from equilibrium by a variety of means. Several mechanisms to excite the system and their relative merits are reviewed. In this talk we focus on the process of exciting electron-glasses by interaction with near infrared radiation. The efficiency of this protocol varies considerably among different electron-glasses, but it only weakly depends on their resistance at liquid helium temperatures. A dramatic enhancement of the excitation efficiency is observed upon doping crystalline indium-oxide with Au. Some enhancement is observed also in samples doped with Pb but this enhancement fades away with time unlike the situation in the Au-doped samples. Several structural and analytical tools are used to characterize the changes in the materials that may be responsible for these effects. Possible routes by which high-frequency electromagnetic fields take the system far from equilibrium are discussed.


Otsutstvie fononov v nekotorykh sluchainykh reshetkakh

14 April 2011 in 11:30

Ya.M. Bel’tyukov, D.A. Parshin (Sankt-Peterburgskii Gosudarstvennyi Politekhnicheskii Universitet)

Teoriya sluchainykh matrits ispol’zovana dlya analiza kolebanii v neuporyadochennykh sistemakh. Issledovana sluchainaya dinamicheskaya matritsa M = AAT , obladayushchaya neotritsatel’nymi sobstvennymi znacheniyami ε = ω2. Matritsa A — proizvol’naya kvadratnaya (N × N), veshchestvennaya sluchainaya matritsa. Rassmotren sluchai, kogda matritsa A zadana na prostoi kubicheskoi reshetke, obladayushchei translyatsionnoi invariantnost’yu (potentsial’naya energiya sistemy zavisit ot raznosti smeshchenii atomov iz polozhenii ravnovesiya) s vzaimodeistviem tol’ko s blizhaishimi sosedyami. Pokazano, chto pri opredelennom tipe besporyadka, dlinnovolnovye goldstounovskie mody (fonony) ne mogut rasprostranyat’sya po reshetke. Plotnost’ kolebatel’nykh sostoyanii g(ω) kak funktsiya chastoty ω ne obrashchaetsya v nol’, pri ω = 0. Prichina takogo anomal’nogo povedeniya zaklyuchaetsya v narushenii affinnosti smeshchenii atomov pri deformatsiyakh reshetki i neprimenimosti k etoi sisteme makroskopicheskoi teorii uprugosti. Modul’ Yunga E ispytyvaet sil’nye fluktuatsii ot obraztsa k obraztsu, zavisit ot razmerov sistemy i obrashchaetsya v nol’ v termodinamicheskom predele. Eto povedenie napominaet svoistva granulyarnykh sred v tochke tak nazyvaemogo jamming transition. Prakticheski vse kolebatel’nye mody v sisteme okazyvayutsya delokalizovannymi i energiya kolebanii rasprostranyaetsya v reshetke posredstvom diffuzii. Etot diffuzionnyi mekhanizm perenosa energii pozvolyaet kachestvenno ob’yasnit’ teploprovodnost’ stekol κ(T) v shirokoi oblasti temperatur T ot 20 — 1000 K.

Three-way junctions of interacting quantum wires: Tunneling into a Luttinger liquid revisited

7 April 2011 in 11:30

Dmitry Polyakov (Institut fuer Nanotechnologie, Karlsruhe Institute of Technology, Germany)

I will first review what makes correlated electron systems in one dimension (for which the Luttinger liquid is a prototype model) special as far as the inelastic scattering processes and the elastic renormalizations are concerned. I will then focus on the question of how interactions renormalize tunneling into a Luttinger liquid without making the usual assumption that the tunneling amplitude is infinitesimally small. It will be shown that the conventional fixed point, which describes the zero-bias suppression of tunneling into a homogeneous liquid, has a finite basin of attraction only in the point-contact model. A finite size of the contact makes it generically unstable to the tunneling-induced breakup of the liquid into two semi-infinite parts. In the course of the renormalization, the tunneling conductance may behave nonmonotonically and the tunnel contact may become more transparent with decreasing temperature or bias voltage. In the point-contact model, the regions on the phase diagram which correspond to the conventional zero-bias anomaly and the breakup are separated by a quantum phase transition. I will put these results in the context of theory of «three-way junctions» of correlated quantum wires.

Effekt Aaronova-Boma na nanootverstiyakh v tonkom grafite i grafene

24 March 2011 in 11:30

Yu. Latyshev (IRE RAN, Moskva)

Issledovano magnetosoprotivlenie monokristallov nanotonkogo grafita (N//c), coderzhashchego nanootverstiya (antidoty), poluchavshiesya libo oblucheniem tyazhelymi ionami v napravlenii osi c (diametr antidota 24 nm), libo s pomoshch’yu fokusirovannykh ionnykh puchkov (diametr 35 nm). Pokazano, chto prisutstvie antidotov na obraztsakh oboikh tipov vyzyvaet poyavlenie ostsilliruyushchego vklada v magnetosoprotivlenie s periodom, sootvetstvuyushchim kvantu magnitnogo potoka hc/e na ploshchad’ antidota i nezavisyashchim ot tolshchiny obraztsa vplot’ do 1 nm (bigrafen). Ostsillyatsii nablyudayutsya do vysokikh temperatur ≈ 50K. Rezul’taty svyazyvayutsya s vkladom poverkhnostnykh grafenovykh sloev i s sushchestvovaniem predskazannykh nedavno kraevykh sostoyanii tammovskogo tipa vokrug antidota, obuslavlivayushchikh nablyudenie effekta Aaronova-Boma na obraztsakh nekol’tsevoi geometrii.

Lokalizovannye pary i psevdoshchel’ vblizi perekhoda sverkhprovodnik-izolyator v amorfnykh sverkhprovodnikakh

10 March 2011 in 11:30

V.F. Gantmakher (ISSP RAS)

Fizicheskii smysl ponyatiya lokalizovannykh sverkhprovodyashchikh par obsuzhdaetsya na osnove analiza povedeniya granulirovannykh sverkhprovodnikov, effekta chetnosti i kharaktera dvizheniya kuperovskikh par v okrestnosti perekhoda Berezinskogo—Kosterlitsa—Taulesa. Eksperimental’nye dokazatel’stva sushchestvovaniya lokalizovannykh par baziruyutsya na izmereniyakh magnetosoprotivleniya i na izmereniyakh plotnosti sostoyanii pri pomoshchi tunnel’nogo mikroskopa. Perekhod sverkhprovodnika v sostoyanie izolyatora mozhet i ne soprovozhdat’sya poyavleniem lokalizovannykh par. Sredi uslovii, sposobstvuyushchikh ikh poyavleniyu, blizost’ k perekhodu metall-izolyator, privodyashchaya k fraktal’nosti volnovykh funktsii elektronov, a takzhe opredelennye korrelyatsii v sluchainom potentsiale.

Magnetic field induced non-Gaussian fluctuations in macroscopic equilibrium systems

24 February 2011 in 11:30

K.E. Nagaev (IRE RAS)

Vychisleny zavisyashchie ot magnitnogo polya nelineinaya provodimost’ i shum v dvumernoi makroskopicheskoi neodnorodnoi sisteme. Esli eta sistema ne obladaet spetsial’noi simmetriei, to pri nalichii magnitnogo polya tretii kumulyant toka otlichen ot nulya dazhe v ravnovesii. On svyazan s pervoi i vtoroi proizvodnoi po napryazheniyu ot spektral’noi plotnosti i srednego toka takimi zhe sootnosheniyami, kak i dlya mezoskopicheskikh kvantovo-kogerentnykh sistem, no sami eti velichiny mogut byt’ gorazdo bol’she. Takim obrazom, sistema predstavlyaet soboi udobnyi ob’ekt dlya proverki nelineinykh fluktuatsionno-dissipatsionnykh sootnoshenii. [arXiv:1004.5310, Phys. Rev. Lett. 105, 146802 (2010)]

Svoistva dvumernykh elektronnykh sistem pod mikrovolnovym oblucheniem

10 February 2011 in 11:30

S.I. Dorozhkin (ISSP RAS)

V eksperimental’noi chasti doklada budut privedeny eksperimental’nye rezul’taty po (1) magnetoostsillyatsiyam fototoka i foto-EDS, nablyudaemym v dvumernykh elektronnykh sistemakh pod mikrovolnovym izlucheniem pri ispol’zovanii kontaktov razlichnoi topologii; (2) nablyudeniyu effekta bistabil’nosti v rezhime indutsirovannogo izlucheniem sostoyaniya dvumernykh elektronnykh sistem, obladayushchego maloi dissipatsiei na postoyannom toka (tak nazyvaemoe «microwave induced zero-resistance state»). Poluchennye rezul’taty svidetel’stvuyut o spontannykh perekhodakh mezhdu dvumya sostoyaniyami s razlichnoi geometriei elektricheskikh polei, indutsirovannykh izlucheniem. Teoreticheskaya chast’ posvyashchena rezul’tatam rascheta foto-gal’vanicheskikh signalov, voznikayushchikh za schet vstroennogo v obraztse elektricheskogo polya, chto trebuet rascheta kak provodimosti, tak i koeffitsienta diffuzii elektronov v neravnovesnykh usloviyakh pod oblucheniem. Pokazano, chto v sluchae, kogda osnovnoi foto-otklik sistemy voznikaet za schet neravnovesnogo zapolneniya elektronnogo spektra, vliyanie izlucheniya na koeffitsient diffuzii malo, tak chto vozmozhno vozniknovenie situatsii, kogda elektronnaya sistema v odnorodnom sostoyanii opisyvaetsya otritsatel’noi provodimost’yu i polozhitel’nym koeffitsientom diffuzii. Polucheny vol’t-ampernye kharakteristiki, kotorye opisyvayut eksperimental’nye rezul’taty. Dlya prostoi geometrii pokazano, chto odnorodnoe sostoyanie konechnoi dvumernoi sistemy s otritsatel’noi provodimost’yu i polozhitel’nym koeffitsientom diffuzii mozhet ostavat’sya ustoichivym. Ustanovleno anomal’noe povedenie ekranirovaniya v takikh usloviyakh.

Fast vortices and superconducting fluctuations in the cuprates and amorphous superconductors

27 January 2011 in 11:30

Peter Armitage (John Hopkins University, Baltimore, USA)

The nature of the underdoped pseudogap regime of the high-temperature superconductors has been a matter of long-term debate. On quite general grounds, one expects that due to their low superfluid densities and short correlation lengths, superconducting fluctuations will be very significant for transport and thermodynamic properties in this part of the phase diagram. Although there is ample experimental evidence for such correlations, there has been disagreement about how high in temperature they may persist, their role in the phenomenology of the pseudogap, and their significance for understanding high-temperature superconductivity. In this work we use THz time-domain spectroscopy (TTDS) to probe the temporal fluctuations of superconductivity above Tc in LSCO thin films over a doping range that spans almost the entire superconducting dome (x=0.06 to 0.25). Signatures of the fluctuations persist in the conductivity in a comparatively narrow temperature range, up to — at most — 16 K above Tc. We compare our results with the measurements of diamagnetism in a similarly doped crystals of LSCO and show through a vortex-plasma model that if the fluctuation diamagnetism solely originates in vortices, then they must necessarily exhibit an anomalously large vortex diffusion constant, which is more than two orders of magnitude larger than the Bardeen-Stephen estimate. This points to either an entirely different character to vortex dynamics in the underdoped d-wave cuprates or a contribution to the diamagnetic response that is not superconducting in origin. I will make a comparison to our related work using broadband microwave spectroscopy on amorphous superconducting InO thing films.

Statistics of energy flows, temperature fluctuations and underlying techniques

7 October 2010 in 11:30

Yu.V. Nazarov (Delft University of Technology, Netherlands)

I will review recent results on statistics of energy flows and temperature fluctuations in zero-dimensional systems with emphasis on underlying techniques. The motivation for this is a recent revival of interest to thermal transport and successes in micro-thermometry. The technique in question has been proposed in 2003 by Kindermann and Pilgram. I will start by putting it into general context. Further, I concentrate on simple model systems and give the details of technique application for concrete setups of double junction and single-electron transistor. I will also shortly address the flows of (quantum) information quantities, the problems arising in this context and possible relation to energy flows.

γ→α fazovyi perekhod v tserii ne yavlyaetsya izostrukturnym: teoriya i eksperiment

30 September 2010 in 11:30

A.V. Nikolaev (NIIYaF MGU, IFKhE RAN), A.V. Tsvyashchenko, A.I. Velichkov, A.V. Salamatin, L.N. Fomicheva, G.K. Ryasnyi, A.A. Sorokin, O.I. Kochetov, M. Budzinskii, K.G. Mishel’

Allotropnye formy odnogo i togo zhe elementa obychno kharakterizuyutsya raznymi gruppami prostranstvennoi simmetrii. Odnako, v tserii obnaruzheny dve termodinamicheski stabil’nye fazy — γ i α, kotorye obladayut odnoi i toi zhe granetsentrirovannoi kubicheskoi (gtsk) reshetkoi i otlichayutsya tol’ko znacheniem ee postoyannoi. S tekh por v techenie 60 let γ→α perekhod v tserii stal prototipom dlya drugikh «izostrukturnykh» fazovykh perekhodov. Dlya ob’yasneniya sushchestvovaniya etikh dvukh faz bylo vydvinuto mnogo teoreticheskikh modelei, v kotorykh vydelyalis’ razlichnye faktory, otvetstvennye za ikh formirovanie. Sredi etikh modelei byla vydvinuta teoriya kvadrupol’nogo uporyadocheniya, kotoraya, v otlichie ot ostal’nykh podkhodov, utverzhdala, chto etot perekhod yavlyaetsya skrytym strukturnym perekhodom, i predlagala proverit’ etot vyvod eksperimental’nym obrazom. V dannom doklade privoditsya kratkii obzor teorii kvadrupol’nogo uporyadocheniya i pervykh eksperimental’nykh dannykh A.V. Tsvyashchenko s soavtorami, kotorye podtverdili etu teoriyu i obnaruzhili, chto fazovyi perekhod ot γ-Ce k α-Ce ne yavlyaetsya izostrukturnym. Ssylki: [1] Elisashberg, G. and Capellmann, H., JETP Lett. 67, 125 (1998). [2] Nikolaev, A.V. and Michel, K. H., Eur. Phys. J. B 9, 619-634 (1999). [3] Nikolaev, A.V. and Michel, K. H., Phys. Rev. B 66, 054103 (2002). [4] Tsvyashenko, A. V. et al., cond-mat arXiv: 1003.1247 (2010).

Dvumernyi fermi-gaz ul’trakholodnykh atomov

23 September 2010 in 11:30

A.V. Turlapov (IPF RAN, Nizhnii Novgorod)

Eksperimenty s ul’trakholodnym gazom fermi-atomov pozvolyayut modelirovat’ fundamental’nye yavleniya kvantovoi fiziki. V tom chisle — yavleniya, ne nablyudavshiesya v drugikh fermi-sistemakh. K takim yavleniyam otnositsya kogerentnyi perekhod mezhdu fermi- i boze-gazom, stabil’nost’ sil’novzaimodeistvuyushchei fermi-sistemy, sverkhtekuchest’ pri rezonansnykh vzaimodeistviyakh, a takzhe, vozmozhno, vyazkost’ vblizi kvantovogo minimuma i bluzhdayushchii ferromagnetizm. Uspekhi v eksperimentakh s ul’trakholodnymi fermi-atomami svyazany s vozmozhnost’yu tochnogo kontrolya i nastroiki parametrov — vzaimodeistviya, plotnosti, temperatury, spinovogo sostava. V IPF RAN sozdana novaya eksperimental’naya sistema — dvumernyi fermi-gaz atomov. Ya rasskazhu o prigotovlenii ul’trakholodnogo gaza i o zadachakh, kotorye v budushchem mogut modelirovat’sya v etoi sisteme. Eksperimental’naya sistema, vozmozhno, pozvolit nablyudat’ fazovye perekhody i kriticheskie tochki, predskazannye dlya dvumernykh fermi-sistem. V chisle zadach 2-mernoi fiziki, potentsial’no dostupnykh dlya issledovaniya — sverkhtekuchest’, perekhod Berezinskogo—Kosterlitsa—Taulesa, ferromagnetizm, zadacha o rasseyanii 2 i 3 tel.

Quantum Factoring Algorithm

16 September 2010 in 11:30

Peter Shor (MIT)

Budet podrobno izlozhen znamenityi kvantovyi algoritm faktorizatsii tselykh chisel (tak nazyvaemyi «algoritm Shora», vozmozhnost’ realizatsii kotorogo stavit pod vopros nadezhnost’ skhemy shifrovaniya RSA, baziruyushcheisya na predpolozhenii ob eksponentsial’noi slozhnosti faktorizatsii na klassicheskom komp’yutere) i korotko obsuzhdeny perspektivy kvantovykh vychislenii v tselom. O Pitere Shore v Vikipedii.

Nonequilibrium coherent dynamics in Charge Density Waves from femto-second optical experiments and their modeling

9 September 2010 in 11:30

S. Brazovskii

Fundamental problems in temporal evolution of symmetry breaking phase transitions span subjects from high energy and cosmology, to condensed matter. The reported new approach [1] is the optical study of a far-from-equilibrium evolution of the electronic charge ordering after a quench caused by an intense laser pulse. Technique of multi-pulse spectroscopy with a femto-second resolution allowed to simultaneously monitor both bosonic and fermionic components, coherent aperiodic undulations of the order parameter, critical slowing down of the collective mode (akin to the Higgs boson), and evolution of the particle-hole gap which is due to the Peierls-BCS mechanism. The numerical modeling with no fitting parameters allowed reproducing the observations, particularly the spatio-temporal distortions («Higgs waves») arising from «earthquakes» — annihilation events of topological defects in depth of the sample. The results give a rare access to the in-situ dynamics of phase transitions. Other results apply to experiments by Latyshev et al. at IREE on nano-junctions of CDW materials. We model the ground state reconstruction with creating and propagation of dislocations in the electronic crystal. [1] In collaboration with D. Mihailovic group at the Jozef Stefan Institute, Ljubljana, Slovenia. R. Yusupov, et al, «Coherent dynamics of macroscopic electronic order through a symmetry breaking transition», Nature Physics, DOI:10.1038/NPHYS1738, on-line.

Kvantovaya zaputannost’ i osnovaniya statisticheskoi mekhaniki

13 May 2010 in 11:30

O.V. Lychkovskii (ITEF)

Состояние открытой квантовой системы, взаимодействующей с большим квантовым резервуаром, в большинстве случаев с течением времени приближается к некоторому равновесному состоянию. Это равновесное состояние может зависеть (вообще говоря) или почти не зависеть (как правило) от начального состояния открытой системы и резервуара, являться или не являться распределением Больцмана-Гиббса, и т.д. В последние два десятилетия был доказан ряд теорем о характере релаксации к равновесному состоянию, опирающихся исключительно на уравнение Шредингера для замкнутой системы. Важную роль в этих теоремах играет понятие квантовой запутанности состояний открытой системы и резервуара, генерируемой взаимодействием между ними. В докладе представлен обзор этих результатов.


Anomalous scaling and solitary waves in systems with non-linear diffusion

29 April 2010 in 11:30

Alex Hansen (Norwegian University of Science and Technology, Trondheim, Norway)

With background in the dynamics of wetting films in porous media under two-phase flow conditions, we discuss a non-linear convective-diffusive equation, local in space and time, describing the thickness of a wetting film. The presence of a non-linear diffusion predicts the existence of fronts as well as shock fronts. Despite the absence of memory effects, solutions in the case of pure non-linear diffusion exhibit an anomalous sub-diffusive scaling. Due to a balance between non-linear diffusion and convection we, furthermore, show that solitary waves appear. For large times they merge into a single solitary wave exhibiting a topological stability. Even though our results concern a specific equation, numerical simulations supports the view that anomalous diffusion and the solitary waves disclosed will be general features in such non-linear convective-diffusive dynamics [A. Hansen, B.-S. Skagerstam and G. Tora, arxiv:1003.3638v1 (2010)].

Lokal’nye matritsy i topologicheskie fazy svobodnykh fermionov

15 April 2010 in 11:30

Alexei Kitaev (Caltech)


Josephson effect in a long diffusive SNS junction in a magnetic field

8 April 2010 in 11:30

Dmitri Ivanov, Benoit Crouzy (EPFL)

We study a diffusive superconductor-normal metal-superconductor (SNS) junction in an external magnetic field. In the limit of a long junction, we find that the properties of such a system depend on the width of the junction relative to the length associated with the magnetic field. We compute the critical width separating the regime of pure decay (narrow junction) and the regime of damped oscillations (wide junction) of the critical current as a function of the magnetic flux through the junction. We find an exponential damping of the current, different from the well know Fraunhofer limit which corresponds to the limit of a tunnel junction. In the limit of a wide junction, the superconducting pair correlations and the critical current become localized near the border of the junction.

Ref: arXiv:0907.0632

Electronic transport in Mach-Zehnder and Fabry-Perot interferometers realized with quantum Hall edge states

1 April 2010 in 11:30

Dmitry Bagrets (INT, Karlsruhe Institute of Technology, Germany)

Motivated by a series of recent experiments I will discuss the influence of the long range Coulomb interaction on the quantum coherence in Mach-Zehnder and Fabry-Perot electronic interferometers realized with integer quantum Hall edge states. I will review the experimental status in this intriguing subfield of mesoscopics and further on will propose a simple physical model which enables to explain an experimentally observed unusual non-monotonic dependence of the visibility of the interference pattern. The origin of this effect is found to be a combination of the electrostatic Aharonov-Bohm effect, related to the charge imbalance on different arms of the interferometer, and the non-equilibrium dephasing, which stems from the emission of out-of-equilibrium plasmons in course of inelastic electron tunneling. The possible role of the edge-state reconstruction on the formation of the interference pattern is also discussed.

Transport impul’sa i massy pri rasprostranennii elektromagnitnoi volny v srede s otritsatel’nym prelomleniem

25 February 2010 in 11:30

V.G. Veselago (Prokhorov GPI, MIPT)

Rassmotren vopros ob impul’se fotona, rasprostranyayushchegosya v prelomlyayushchei srede. Pokazano, chto v etom sluchae sootnosheniya P = hk i ΔM = E/c2 ne mogut byt’ realizovany odnovremenno. Pokazano, chto v srede s otritsatel’nym prelomleniem svetovoe davlenie zamenyaetsya na svetovoe prityazhenie.

Vzaimodeistviya, korrelirovannye sostoyaniya i spin-dolinnaya simmetriya v dvukhsloinom grafene

18 February 2010 in 11:30

L. Levitov (MIT)

We analyze competition between different ordered states in bilayer graphene (BLG). Combining arguments based on SU(4) flavor symmetry with a mean field analysis, we identify the lowest energy state with the anomalous Hall insulator (AHI). This state is an SU(4) singlet excitonic insulator with broken time reversal symmetry, exhibiting quantized Hall effect in the absence of external magnetic field. Applied electric field drives an Ising-type phase transition, restoring time reversal symmetry. Applied magnetic field drives a transition from the AHI state to a quantum Hall ferromagnet state. We estimate energies of these ordered states, taking full account of screening, and predict the phase diagram.

Superinsulating state in two-dimensional superconducting systems: experiment and theory

28 January 2010 in 11:30

T. Baturina (IFP SO RAN, Novosibirsk), N. Shchelkachyov (ITF), V. Vinokur (Argonne National Laboratory, USA)

We discuss the results of the experimental study of two-dimensional superconducting systems (TiN films and Josephson junction arrays) in the vicinity of the superconductor-insulator transition. We have found the transition from the activation-type conductivity characteristic to insulating state to the state with the practically zero conductivity. Experimental findings indicate that the observed superinsulating state is the low-temperature phase of the charge Berezinskii-Kosterlitz-Thouless (BKT) transition. Considering the charge transfer in two-dimensional Josephson junction arrays, we observe that the tunneling current in their insulating state is ensured by the relaxation mediated by the electron-hole environment. The energy gap, appearing in the electron-hole spectrum below the BKT transition, gives rise to suppression of the tunneling current offering the microscopic mechanism for the superinsulating behavior.

Zaputannye sostoyaniya elektronov v sverkhprovodnikakh i normal’nykh metallakh

17 December 2009 in 11:30

G.B. Lesovik

Zaputannye sostoyaniya igrayut klyuchevuyu rol’ v kvantovoi kriptografii i kvantovykh vychisleniyakh. Krome togo, izuchenie stepeni zaputannosti stalo v poslednee vremya novym instrumentom izucheniya mnogochastichnykh sistem. Zaputannye sostoyaniya fotonov realizovany mnogo let nazad i uzhe ispol’zuyutsya v prakticheskoi kvantovoi kriptografii. V to zhe vremya zaputannye sostoyaniya elektronov eksperimental’no poka ne nablyudalis’. My obsudim teoreticheskie predlozheniya po nablyudeniyu zaputannosti elektronov v kvantovykh provodnikakh. My takzhe obsudim sposoby nablyudeniya zaputannosti i eksperiment, sdelannyi nedavno v SShA (Wei, Chandrasekhar, arXiv:0910.5558), v kotorom nablyudalos’ perekryostnoe Andreevskoe otrazhenie, a takzhe perekryostnye polozhitel’nye korrelyatsii tokov. Etot eksperiment yavlyaetsya kosvennym ukazaniem na to, chto Kuperovskaya para, vyletaya iz sverkhprovodnika, raspadaetsya na dva zaputannykh mezhdu soboi elektrona, kotorye napravlyayutsya v normal’nyi provodnik cherez dva raznykh kontakta

Tunntling into the nonequilibrium state of the Luttinger liquid

5 November 2009 in 11:30

D. Bagrets (Institut fuer Nanotechnologie, Forschungszentrum Karlsruhe, Germany)

will discuss the problem of tunneling into the voltage biased quantum wire containing weak backscattering defects. I will argue that one-dimensional interacting electrons in such a wire constitute a true non-equilibrium state of the Luttinger liquid (LL). This state is created as the result of inelastic electron backscattering leading to emission of non-equilibrium plasmons with typical frequency of the order of applied voltage eU. Tunneling rates of electron into/from such state are split into two edges. I show that a tunneling exponent of the main edge at the Fermi energy (EF) is positive and is that of a bulk exponent in the equilibrium LL, while the power law exponent at the side edge at EFeU turns out to be negative if Coulomb interaction is not too strong.

Statisticheskaya struktura kvantovoi teorii

22 October 2009 in 11:30

A.S. Kholevo (MIRAN)

Za poslednie tri desyatiletiya v matematicheskikh osnovaniyakh kvantovoi mekhaniki, svyazannykh s teoriei kvantovykh izmerenii, proizoshli glubokie peremeny. V nastoyashchee vremya razvorachivaetsya ikh shirokoe osmyslenie. Khorosho izvestno, chto kvantovaya mekhanika - eto ne prosto dinamicheskaya teoriya; snabzhennaya statisticheskoi interpretatsiei, ona porozhdaet novyi vid veroyatnostnoi modeli, radikal’no otlichayushcheisya ot klassicheskoi. Takim obrazom, statisticheskaya struktura kvantovoi mekhaniki yavlyaetsya predmetom, zasluzhivayushchim spetsial’nogo izucheniya i v bol’shoi stepeni otlichayushchimsya ot standartnogo soderzhaniya knig po kvantovoi mekhanike. Poyavlenie prikladnykh napravlenii kvantovoi fiziki, takikh kak kvantovaya optika, kvantovaya elektronika i opticheskaya svyaz’, a takzhe razvitie tekhniki vysokotochnogo eksperimenta vyzvali novyi interes k kvantovym izmereniyam i pereveli vopros o posledovatel’noi kolichestvennoi kvantovoi statisticheskoi teorii izmerenii v prakticheskuyu ploskost’. Takaya teoriya byla sozdana v poslednei chetverti proshlogo veka kak daleko idushchee logicheskoe razvitie statisticheskoi interpretatsii, opirayushcheesya na osnovanie sovremennogo funktsional’nogo analiza. Perefraziruya izvestnoe opredelenie teorii veroyatnostei («Probability theory is a measure theory - with a soul», M. Kac), mozhno skazat’, chto eto - teoriya operatorov v gil’bertovom prostranstve, «odushevlennaya» statisticheskoi interpretatsiei kvantovoi mekhaniki. Matematicheskoi sushchnost’yu etoi teorii yavlyayutsya raznoobraznye aspekty polozhitel’nosti i tenzornykh proizvedenii v algebrakh operatorov (imeyushchie svoi korni, sootvetstvenno, v fundamental’nykh veroyatnostnykh svoistvakh polozhitel’nosti i nezavisimosti). V doklade budet dan obzor osnovnykh napravlenii v sovremennykh issledovaniyakh statisticheskoi struktury kvantovoi teorii.

Veroyatnostnoe predstavlenie kvantovoi mekhaniki

1 October 2009 in 11:30

V.I. Man’ko (FIAN)

Dana formulirovka kvantovoi mekhaniki (tak nazyvaemoe veroyatnostnoe predstavlenie), v kotoroi kvantovye sostoyaniya opisyvayutsya raspredeleniyami veroyatnostei kak v klassicheskoi statisticheskoi mekhanike dlya sistem s nepreryvnymi peremennymi (koordinata i impul’s), tak i dlya sistem s diskretnymi peremennymi (spiny, dvukhurovnevye atomy, kubity i kudity). Osnovnoe evolyutsionnoe uravnenie i uravnenie dlya urovnya energii dany dlya matritsy plotnosti (uravnenie fon Neimana) i v fazovom prostranstve (uravnenie Moiala), a takzhe dlya raspredelenii veroyatnostei v veroyatnostnom predstavlenii kvantovoi mekhaniki, chto sravnivaetsya s klassicheskim kineticheskim uravneniem Liuvillya. Vyvodyatsya sootnosheniya neopredelyonnostei Geizenberga i Shryodingera-Robertsona i pokazany ikh obobshcheniya dlya smeshannykh sostoyanii v forme, dopuskayushchei pryamuyu eksperimental’nuyu proverku v eksperimentakh kvantovoi optiki, v kotorykh izmeryaetsya volnovaya funktsiya. Neravenstva Bella ob’yasnyayutsya dlya veroyatnostnogo opisaniya sostoyanii spina. Obsuzhdayutsya perspektivy polucheniya novykh rezul’tatov s ispol’zovaniem nedavno naidennogo veroyatnostnogo predstavleniya kvantovykh sostoyanii.

Zaputannost’ sostoyanii, koty Shryodingera i nelokal’nost’ v kvantovoi mekhanike

24 September 2009 in 11:30

V.I. Man’ko (FIAN)

Ob’yasnyaetsya ponyatie kvantovykh korrelyatsii i fenomen zaputannosti mnogochastichnykh kvantovykh sistem. Predstavlyaetsya kontseptsiya chistykh kvantovykh sostoyanii v terminakh volnovoi funktsii (Shryodinger, 1926) i smeshannykh kvantovykh sostoyanii v terminakh matritsy plotnosti (Landau, fon Neiman, 1927), kotoraya sravnivaetsya s kontseptsiei sostoyanii v klassicheskoi statisticheskoi mekhanike. Rasskazyvaetsya ob integralakh dvizheniya dlya sistem s nestatsionarnymi gamil’tonianami i rassmotren primer parametricheskogo ostsillyatora. Rassmotreno sovremennoe sostoyanie diskussii, kasayushcheisya problemy skrytykh parametrov i paradoksa Einshteina-Podol’skogo-Rozena. Neravenstva Bella obsuzhdayutsya dlya klassicheskoi granitsy 2. Obsuzhdaetsya granitsa Tsirel’sona 2*21/2. Predstavleny primery superpozitsii ili kotov Shryodingera, skonstruirovannykh iz kogerentnykh sostoyanii, takie kak chyotnye i nechyotnye kogerentnye sostoyaniya. Zadayutsya szhatye sostoyaniya fotonov (fononov) i ikh statistika. Dano opisanie fazovogo prostranstva v kvantovoi mekhanike v terminakh funktsii Vignera, vvedyonnoi v 1932, funktsii Khusimi, vvedyonnoi v 1940, i diagonal’nogo predstavleniya Sudarshana-Glaubera, vvedyonnogo v 1963, chto sravnivaetsya «na pal’tsakh» s tak nazyvaemym kvantovaniem so zvyozdochnym proizvedeniem.

Tonkaya struktura rezonansov Aronova-Boma v kvantovom kol’tse s Lattinzherovskoi zhidkost’yu

10 September 2009 in 11:30

V.Yu. Kachorovskii (FTI im. Ioffe, SPb), A.P. Dmitriev, I.V. Gornyi, D.G. Polyakov

Rasschitan interferentsionnyi vklad v tunnel’nyi kondaktans kvantovogo odnokanal’nogo kol’tsa s besspinovymi elektronami, vzaimodeistvuyushchimi v ramkakh modeli Lattinzhera, i issledovana ego zavisimost’ ot temperatury i magnitnogo potoka, pronizyvayushchego kol’tso. V otsutstvii elektron-elektronnogo vzaimodeistviya interferentsionnyi kondaktans soderzhit seriyu rezonansov Aaronova-Boma. Pokazano, chto vzaimodeistvie privodit k rasshchepleniyu kazhdogo rezonansa v gruppu uzkikh pikov, rasstoyanie mezhdu kotorymi proportsional’no sile vzaimodeistviya. Razmernoe kvantovanie v kol’tse privodit k sil’nomu podavleniyu sboya fazy za schet elektron-elektronnogo vzaimodeistviya dazhe pri otnositel’no vysokoi temperature, znachitel’no prevyshayushchei rasstoyanie mezhdu kvantovymi urovnyami v kol’tse. Poetomu shirina voznikayushchikh pikov v osnovnom opredelyaetsya dvumya faktorami: vremenem tunnel’nogo vykhoda iz sistemy i temperaturoi, no ne siloi vzaimodeistviya.

Ubyvanie koeffitsientov fur’e reshenii sistemy Nav’e-Stoksa

3 September 2009 in 11:30

Ya.G. Sinai

Perekryostnoe andreevskoe otrazhenie v geterostrukturakh

16 April 2009 in 11:30

Mikhail Kalenkov (FIAN)

V doklade budut predstavleny teoreticheskie rezul’taty po elektronnomu transportu v trekhterminal’nykh geterostrukturakh normal’nyi metall/sverkhprovodnik/normal’nyi metall. V takikh sistemakh elektron, padayushchii iz normal’nogo elektroda v sverkhprovodnik, mozhet otrazit’sya v vide dyrki v drugoi normal’nyi elektrod. Etot protsess, nazyvaemyi perekrestnym andreevskim otrazheniem, naravne s obychnym tunnelirovaniem, opredelyaet nelokal’nyi kondaktans v rassmatrivaemoi geterostrukture. V ramkakh kvaziklassicheskoi teorii sverkhprovodimosti polucheny formuly dlya vol’t-ampernykh kharakteristik kak v ballisticheskom priblizhenii, tak i v diffuzionnom predele. Budet provedeno sravnenie razvitoi teorii s rezul’tatami nedavnikh eksperimentov.

Spontaneous symmetry breaking in general relativity. Brane world concept

9 April 2009 in 11:30

B.E. Meierovich (P.L. Kapitza Institute for Physical Problems)

Gravitational properties of a hedge-hog type topological defect in two extra dimensions are considered in General Relativity employing a vector as the order parameter. The developed macroscopic theory of phase transitions with spontaneous symmetry breaking is applied to the analysis of possible «thick» brane structures. The previous considerations were done using the order parameter in the form of a multiplet in a target space of scalar fields. The difference of these two approaches is analyzed and demonstrated in detail. There are two different symmetries of regular solutions of Einstein equations for a hedgehog type vector order parameter. Both solutions are analyzed in parallel analytically and numerically. Regular configurations in cases of vector order parameter have one more free parameter in comparison with the scalar multiplet solutions. It is shown that the existence of a negative cosmological constant is sufficient for the spontaneous symmetry breaking of the initially plain bulk. Regular configurations have a growing gravitational potential and are able to trap the matter to the brane. Among others there are solutions with the gravitational potential having several points of minimum. Identical in the uniform bulk spin-less particles, being trapped within separate points of minimum, acquire different masses and appear to an observer within the brane as different particles with integer spins.

Elektricheskoe dipol’noe ekho v steklakh v magnitnom pole

26 February 2009 in 11:30

D.A. Parshin (Sankt-Peterburgskii gosudarstvennyi politekhnicheskii universitet)

Provedeno teoreticheskoe rassmotrenie vliyaniya magnitnogo polya na amplitudu dipol’nogo ekha v steklakh pri temperaturakh poryadka 10 mK, obuslovlennogo nalichiem v stekle nesfericheskikh yader s elektricheskimi kvadrupol’nymi momentami. Pokazano, chto v etom sluchae dvukhurovnevye sistemy (DUS), opredelyayushchie svoistva stekol pri nizkikh temperaturakh, prevrashchayutsya v bolee slozhnye - mnogourovnevye sistemy. Eti sistemy obladayut novymi (po sravneniyu s obychnymi DUS) svoistvami, naprimer, ostsillyatsiyami amplitudy elektricheskogo dipol’nogo ekha v magnitnom pole. Eti ostsillyatsii (khotya i sushchestvenno men’shei amplitudy) sokhranyayutsya i v tom sluchae, kogda v stekle nesfericheskikh yader net (glitserol). V etom sluchae za nikh otvetstvenno slaboe dipol’-dipol’noe vzaimodeistvie magnitnykh momentov yader. V ramkakh teorii vozmushchenii vyvedena obshchaya formula, opisyvayushchaya amplitudu ekha v proizvol’no rasshcheplennoi DUS. V rabote proveden detal’nyi analiticheskii i chislennyi analiz etoi formuly. Polucheno khoroshee kachestvennoe i kolichestvennoe soglasie teorii s eksperimental’nymi dannymi.

Spin-orbital’naya svyaz’ i mezhelektronnoe vzaimodeistvie v poluprovodnikakh

19 February 2009 in 11:30

M.M. Glazov (Fiziko-tekhnicheskii institut im. A.F. Ioffe RAN)

Doklad posvyashchen spin-orbital’nym effektam v elektron-elektronnom vzaimodeistvii i ikh proyavleniyam v poluprovodnikovykh nanostrukturakh. V ramkakh kp-metoda teorii vozmushchenii polucheny vyrazheniya dlya spin-zavisimykh vkladov v effektivnyi matrichnyi element mezhelektronnogo rasseyaniya. Obsuzhdaetsya spinovaya relaksatsiya elektronov i vozmozhnost’ generatsii chisto spinovykh tokov za schet elektron-elektronnogo vzaimodeistviya. Analiziruetsya tonkaya struktura dvukh elektronov, lokalizovannykh v poluprovodnikovoi kvantovoi tochke, obuslovlennaya spin-orbital’nymi vkladami v elektron-elektronnoe vzaimodeistvie. Pokazano, chto v anizotropnykh kvantovykh tochkakh spinovoe vyrozhdenie tripletnogo sostoyaniya pary nositelei polnost’yu snyato. Obsuzhdayutsya zavisimosti rasshcheplenii spektra ot geometricheskikh parametrov kvantovykh tochek, a takzhe vozmozhnye proyavleniya tonkoi struktury pary nositelei v spektrakh fotolyuminestsentsii kvantovykh tochek. [1] M.M. Glazov, V.D. Kulakovskii, Preprint arXiv:0901.2893 (2009).

Kramers degeneracy in a magnetic field and zeeman spin-orbit coupling in antiferromagnets

12 February 2009 in 11:30

Revaz Ramazashvili (Orsay University)

Essential dependence of the electron g-tensor on the quasiparticle momentum is a fundamental and, so far, largely overlooked property of antiferromagnetic conductors. I will discuss some of its symmetry underpinnings and experimental consequences. The predictions may be relevant to antiferromagnetic conductors from chromium to electron- and hole-doped cuprates, borocarbides, pnictides, organic and heavy fermion antiferromagnets.

Optika metamaterialov

15 January 2009 in 11:30

A.K. Sarychev (Institut teoreticheskoi i prikladnoi elektrodinamiki RAN)

Odnim iz naibolee interesnykh rezul’tatov v fizike poslednego vremeni yavlyaetsya sozdanie i issledovanie opticheskikh metamaterialov. Strogo govorya, termin «metamaterial» oznachaet vsego lish’ «iskusstvenno sozdannoe veshchestvo». V nanotekhnologiyakh im chashche vsego oboznachayut iskusstvennoe veshchestvo, priobretayushchee neobychnye opticheskie svoistva blagodarya vneseniyu v nego massiva nanometrovykh metallicheskikh chastits. Sozdannye metamaterialy s otritsatel’noi dielektricheskoi pronitsaemost’yu i otritsatel’noi magnitnoi pronitsaemost’yu dayut otritsatel’nyi pokazatel’ prelomleniya. Iz metamaterialov mozhno postroit’ sverkhlinzu, dayushchuyu izobrazhenie nanoob’ektov, nevidimykh v obychnyi mikroskop. S drugoi storony, ekrany, izgotovlennye iz metamaterialov, mogut delat’ ob’ekty nevidimymi. V doklade budet sdelan obzor rabot po opticheskim metamaterilam. Budut rassmotreny traditsionnye metamaterialy, predstavlyayushchie periodicheskie prostranstvennye struktury, sostoyashchie iz rezonansnykh elementov, rol’ kotorykh mogut igrat’ metallicheskie nanoantenny. Razmer nanorezonatorov i rasstoyanie mezhdu nimi predpolagaetsya mnogo men’shim chem dlina volny. Rezonatory obladayut elektricheskim i/ili magnitnym rezonansom. Svoistva rezonansov ob’yasnyayutsya rasprostraneniem opticheskikh plazmonov v metallicheskikh nanostrukturakh. Vysokodobrotnyi elektricheskii rezonans obespechivaet otritsatel’nuyu dielektricheskuyu vospriimchivost’ na chastotakh bol’she rezonansa, a magnitnyi rezonans daet otritsatel’nuyu magnitnuyu vospriimchivost’. Osnovnoi problemoi v prakticheskom primenenii metamaterialov yavlyayutsya omicheskie poteri. My rassmotrim aktivnye metamaterialy, v kotorykh poteri kompensiruyutsya za schet dobavleniya aktivnoi, lazernoi sredy. Aktivnye metamaterialy ispol’zuyutsya dlya konstruirovaniya plazmonnykh nanolazerov i drugikh opticheskikh ustroistv.

Dvumernyi polumetall v kvantovykh yamakh na osnove HgTe

4 December 2008 in 11:30

Z.D. Kvon (Institut fiziki poluprovodnikov SO RAN, Novosibirsk)

V doklade izlagayutsya rezul’taty eksperimental’nogo izucheniya svoistv dvumernogo polumetalla, vpervye realizovannogo blagodarya osobennostyam razmernogo kvantovaniya elektrona v HgTe kvantovykh yamakh. Pokazano, chto on voznikaet v kvantovykh yamakh s orientatsiei (013) i obuslovlen perekrytiem zony provodimosti, dno kotoroi raspolozheno v tsentre dvumernoi zony Brillyuena i valentnoi zony, potolok kotoroi nakhoditsya v bokovykh tochkakh etoi zhe zony. Perekrytie zon sostavlyaet velichinu poryadka 10 meV. Ukazannaya sistema pozvolyaet realizovat’ dvumernyi polumetall s lyubym sootnosheniem mezhdu kontsentratsiei elektronov i dyrok prostym izmeneniem zatvornogo napryazheniya. Obnaruzhen ryad osobennostei, svyazannykh s odnovremennym sushchestvovaniem dvumernykh elektronov (DE) i dyrok (DD) i, v chastnosti, sil’noe rasseyaniem mezhdu elektronnoi i dyrochnoi poverkhnostyami Fermi i anomal’nyi rost provodimosti dvumernogo polumetalla s ponizheniem temperatury, vyzvannyi rasseyaniem dvumernykh elektronov na bolee tyazhelykh dvumernykh dyrkakh. Issledovan perekhod kvantovaya khollovskaya zhidkost’ - izolyator v dvumernom polumetalle. Ego analiz pokazyvaet, chto perekhod nosit kharakter nepreryvnogo kvantovogo fazovogo perekhoda. Ustanovleno, izolyator voznikaet v tochke ravenstva kontsentratsii DE i DD. Na osnove etogo sdelan vyvod o vozmozhnom formirovanii eksitonnogo izolyatora v dannoi tochke.

Nonequilibrium kinetics of a disordered Luttinger liquid

20 November 2008 in 11:30

Dmitry Bagrets (Institut fur Nanotechnologie, Forschungszentrum Karlsruhe, Karlsruhe, Germany)

We develop a kinetic theory for strongly correlated one-dimensional electron systems out of equilibrium, within the framework of the Luttinger liquid model. In the absence of disorder (backscattering off impurities), the model is completely integrable and as such exhibits no relaxation to equilibrium. We formulate a theoretical framework to study relaxation processes due to the interplay of disorder and electron-electron interactions, based on kinetic equations for electron and plasmon distribution functions. We calculate the rate of energy relaxation (equilibration) in a disordered Luttinger liquid, relevant to the transport properties of quantum wires at finite bias voltage. Remarkably, for not too low temperature and bias, the energy-relaxation rate is found to be given by the rate of elastic scattering off disorder, independent of the strength of electron-electron interaction and temperature.

Elektronnaya struktura, magnetizm i sverkhprovodimost’ v ferropniktidakh

16 October 2008 in 11:30

I.I. Mazin (Naval Research Laboratory, USA)

V doklade budet sdelan kratkii obzor naibolee neponyatnykh i neozhidannykh nablyudenii (eksperimental’nykh i chislennykh) kasayushchikhsya novykh sverkhprovodnikov na baze FeAs. Ya rasskazhu o tom, kak v predpolozhenii spin-fluktuatsionnogo mekhanizma poyavlyaetsya neobychnoe sverkhprovodyashchee sostoyanie s s-simmetriei i parametrom poryadka, menyayushchim znak. Vtoraya polovina doklada budet posvyashchena vozmozhnomu ob’yasneniyu magnitnykh, strukturnykh i transportnykh svoistv v normal’nom sostoyanii i obsuzhdeniyu vozmozhnosti nalichiya magnitnogo poryadka dazhe v sverkhprovodyashchikh obraztsakh.

Eksperimental’naya realizatsiya interferometra tipa Fabri-Pero dlya elektronov v rezhime tselochislennogo i drobnogo kvantovogo effekta Kholla

18 September 2008 in 11:30

E.V. Devyatov (IFTT RAN)

Interferometr tipa Fabri-Pero eksperimental’no realizovan dlya elektronov v rezhime kvantovogo effekta Kholla. Interferentsionnye usloviya sozdayutsya dlya elektronov, rasprostranyayushchikhsya v odnom napravlenii na myagkom krayu dvumernoi elektronnoi sistemy. Ispol’zovannaya eksperimental’naya geometriya pozvolyaet kak eksperimental’no podtverdit’ myagkost’ kraya (nalichie polos szhimaemoi i neszhimaemoi elektronnoi zhidkosti), tak i issledovat’ interferentsionnye effekty, svyazannye s transportom poperek otdel’noi neszhimaemoi polosy. Pokazano nalichie interferentsii pri transporte poperek polosok s tselochislennym faktorom zapolneniya i drobnymi faktorami, ne otnosyashchimisya k osnovnoi laflinovskoi posledovatel’nosti. Poluchennye rezul’taty oznachayut, chto interferentsiya opredelyaetsya «normal’nymi» elektronami dazhe v rezhime drobnogo kvantovogo effekta Kholla. Obsuzhdaetsya vliyanie ekranirovki na amplitudu i period interferentsionnykh ostsillyatsii.

Gluon scattering in supersymmetric Yang-Mills theory and quantum geometry of the momentum space

15 May 2008 in 11:30

Aleksandr Gorskii (ITEF)

Poluprovodnikovaya elektronika na osnove karbida kremniya (SiC): sovremennoe sostoyanie i perspektivy

24 April 2008 in 11:30

A.A. Lebedev (Laboratoriya fiziki poluprovodnikovykh priborov FTI RAN im. A.F. Ioffe)

Istoriya issledovanii SiC. Otkrytie tverdotel’noi elektrolyuminestsentsii. Raboty O.V.Loseva. Preimushchestva SiC pered drugimi poluprovodnikami dlya razrabotki silovoi i SVCh tekhniki. Raboty FTI RAN 60-90kh gg. - metod sublimatsionnoi epitaksii, svetodiody, diody, polevye tranzistory. Politipizm karbida kremniya. Struktura i svoistva razlichnykh politipov. Estestvennaya sverkhreshetka geksagonal’nykh politipov. Transformatsii politipa SiC v protsesse epitaksii. Nekontroliruemoe obrazovanie prosloek (kvantovykh yam) kubicheskogo SiC (3C-SiC) v geksagonal’nom SiC. Degradatsiya priborov na osnove geksagonal’nogo SiC i bor’ba s nei. Poluchenie i issledovanie plenok 3C-SiC na osnove podlozhek drugikh politipov SiC - dvoinikovanie, perekhod metall-izolyator, otritsatel’noe magnetosoprotivlenie. Kontroliruemoe poluchenie SiC geteropolitipnykh struktur. Spontannaya polyarizatsiya. Formirovanie geterostruktur 3S-SiC - nH-SiC metodom sublimatsii v vakuume. Elektrolyuminestsentsiya geterodiodov (p) 3C-SiC / (n) 6H-SiC. Formirovanie nanouglerodnykh plenok na poverkhnosti karbida kremniya v protsesse ego termodestruktsii.

f(R) models of dark energy in the Universe

10 April 2008 in 11:30

A. AlexeiStarobinsky

Recent progress in construction of viable dark energy models in f(R) gravity (where R is the scalar curvature) satisfying laboratory, Solar system and cosmological tests is discussed. This class of models represents an interesting alternative to the standard cosmological model with a cosmological constant. Further problems and most critical tests for this approach are outlined.

Mezhsloevaya tunnel’naya spektroskopiya sloistykh soedinenii s volnoi zaryadovoi plotnosti i grafita

3 April 2008 in 11:30

Yurii Latyshev (IRE RAN, Moskva)

Metod mezhsloevogo tunnelirovaniya, shiroko rasprostranennyi dlya spektroskopii sloistykh vysokotemperaturnykh sverkhprovodnikov, ispol’zovan dlya spektroskopii sloistykh materialov s volnoi zaryadovoi plotnosti (VZP) i grafita. S ego pomoshch’yu provedena spektroskopiya energeticheskoi shcheli VZP, v tom chisle v sil’nykh magnitnykh polyakh do 55 Tl. Na grafite provedena spektroskopiya urovnei Landau i pokazan ikh relyativistskii kharakter, prisushchii grafenu.

On statistical mechanics of a single particle in random logarithmically-correlated potentials

20 March 2008 in 11:30

Yan Fyodorov (Nottingham)

I am going to discuss recent results (obtained in collaboration with J.-P. Bouchaud) of the replica approach to statistical mechanics of a single classical particle placed in a random Gaussian landscape. Particular attention will be paid to landscapes with logarithmically growing correlations which give rise to a multifractal structure of the Boltzmann-Gibbs weights. In the limit of infinite spatial dimension we will show that the model is precisely equivalent to the Derrida’s GREM. If time allows, I will also briefly discuss a one-dimensional variant of the model which can be analyzed by a mapping to the Dyson’s Coulomb gas. In particular, in the latter case we conjecture the explicit form of the distribution of the lowest minimum in such a potential.

OPISANIE STATISTIKI PERENOSA ZARYaDA NA YaZYKE VOLNOVYKh FUNKTsII (po materialam rabot v soavtorstve s Dzhanni Blatterom (ETH Zurich), Fabianom Khasslerom (ETH Zurich), Andreem Lebedevym (ITF im. L.D. Landau), Zh.-M. Grafom (ETH Zurich), Mikhailom Suslovym (IFTT), Mikhailom Lebedevym (IFTT))

21 February 2008 in 11:30

G.B. Lesovik

My rassmotrim perenos zaryada v kvantovykh provodnikakh v usloviyakh, kogda na rasseivatel’ iz rezervuara naletaet konechnoe chislo elektronov. V etikh usloviyakh okazyvaetsya ochen’ udobnym opisyvat’ statistiku perenosa na yazyke volnovykh funktsii. My pokazhem, chto kharakteristicheskaya funktsiya, sootvetstvuyushchaya funktsii raspredeleniya perenesennogo zaryada, okazyvaetsya ravnoi tak nazyvaemoi «fidel’nosti», kotoraya s tekhnicheskoi tochki zreniya est’ skalyarnoe proizvedenie dvukh vektorov sostoyanii (volnovykh funktsii), evolyutsionirovavshikh v techenie vremeni izmereniya v razlichnykh usloviyakh. Takaya velichina obychno ispol’zuetsya dlya kharakteristiki stepeni chuvstvitel’nosti evolyutsii kvantovoi sistemy k malym vozmushcheniyam. Etu velichinu mozhno vychislit’ v obshchem vide dlya sluchaya, kogda iskhodnoe sostoyanie elektronov opisyvaetsya determinantom Sletera. (Klyuchevym v etom vychislenii yavlyaetsya to obstoyatel’stvo, chto sostoyanie, opisyvaemoe nekotorym determinantom Sletera, invariantno otnositel’no lineinykh preobrazovanii nabora «vektorov», iz kotorykh sostavlen determinant.) Poluchennoe vyrazhenie dlya kharakteristicheskoi funktsii fakticheski sootvetstvuet tak nazyvaemoi «determinantnoi» formule, izvestnoi s 1993 goda (Levitov, Lesovik). My obsudim obobshchenie ranee poluchennykh formul dlya predela bol’shogo kolichestva elektronov s pomoshch’yu teoremy Stsego (Szego) (obobshchenie na korotkie vremena, i zavisyashchie ot energii prozrachnosti). Dlya sluchaya, kogda iskhodnoe sostoyanie ne opisyvaetsya prostym determinantom Sletera, t.e. yavlyaetsya zaputannym, obshchego vyrazheniya ne sushchestvuet, no mozhno vypisat’ otvety dlya sluchaya, kogda sostoyanie est’ superpozitsiya vsego dvukh determinantov. My osobenno podrobno rassmotrim sluchai dvukh elektronov, opishem razlichnye obmennye effekty v statistike perenosa, ranee ne izuchavshiesya. My takzhe rassmotrim vozmozhnye ogranicheniya na tip funktsii raspredelenii v zavisimosti ot togo, yavlyaetsya li sostoyanie elektronov zaputannym. Nakonets, my obsudim primer zaputannogo sostoyaniya dvukh elektronov, voznikayushchego pri rasseyanii na kvantovoi tochke s uchetom kulonovskogo vzaimodeistviya.

Computational investigation of short pulse laser irradiation with metals

14 February 2008 in 11:30

Zhibin Lin (University of Virginia, USA)

Short pulse laser irradiation with metals has been investigated using a computational method combining the Two-Temperature-Model (TTM) with Molecular Dynamic (MD). In this talk, short pulse laser-induced thermoelastic deformation, generation of crystal defects and ultrafast melting in several metal targets obtained in the computer simulations will be presented. Transient changes in the thermophysical properties, namely the electron-phonon coupling and the electron heat capacity, due to strong laser excitation will be discussed within the framework of Density Functional Theory.

Dopustimaya statistika perenosa zaryada mezhdu provodnikami, soedinennymi zavisyashchim ot vremeni rasseivatelem

7 February 2008 in 11:30

A.G. Abanov, D.A. Ivanov

Naideny ogranicheniya na statistiku perenosa zaryada mezhdu dvumya provodnikami dlya proizvol’noi vremennoi zavisimosti mgnovennoi matritsy rasseyaniya v modeli nevzaimodeistvuyushchikh fermionov pri nulevoi temperature. Ogranicheniya sformulirovany v terminakh analiticheskikh svoistv proizvodyashchei funktsii: ee nuli dolzhny nakhodit’sya na otritsatel’noi deistvitel’noi poluosi. Eta rabota obobshchaet sushchestvuyushchie rezul’taty dlya sluchaya rasseyaniya na statsionarnom rasseivatele pod deistviem napryazheniya, zavisyashchego ot vremeni.

Kollektivnye vozbuzhdeniya v polyarizovannoi kvantovo-khollovskoi sisteme pri ul’traslabom magnitnom dopirovanii

24 January 2008 in 11:30

S. Dikman, V. Flerov, K. Kikoin

Pri ochen’ nizkoi kontsentratsii magnitnoi primesi (Mn) dvumernyi elektronnyi gaz (2DEG) v geterostrukturakh na osnove GaAs dolzhen sokhranyat’ svoi unikal’nye svoistva, opredelyaemye mezhelektronnym vzaimodeistviem, odnovremenno priobretaya magnitnye svoistva, opredelyaemye vzaimodeistviem s primesyami. V rabote issledovan sluchai poluzapolnennogo urovnya Landau v sil’nom magnitnom pole, kogda kvantovo-khollovskaya sistema v osnovnom sostoyanii polyarizovana. Kollektivnye effekty , takie, naprimer, kak poyavlenie lokalizovannykh spinovykh voln, opredelyayutsya sootnosheniem dvukh parametrov - kharakternoi energiei vzaimodeistviya elektronov v 2DEG i energiei nepryamogo obmena d-elektronov primesi, voznikayushchego iz-za ikh gibridizatsii s elektronami 2DEG. Pri otritsatel’nom g-faktore elektronov 2DEG (t.e. v normal’nom, nenapryazhennom sostoyanii GaAs) issleduetsya spektr razlichnykh kollektivnykh sostoyanii, obuslovlennykh prisutstviem primesi. Dostatochno mnogoobraznaya kartina takikh vozbuzhdenii voznikaet iz-za znachitel’nogo chisla razlichnykh proektsii spina iona Mn++, imeyushchego poluzapolnennuyu d-obolochku (t.e. polnyi spin 5/2). Pri otritsatel’nom g-faktore 2DEG mozhet proizoiti sushchestvennaya perestroika osnovnogo sostoyaniya 2DEG dazhe pri nichtozhnoi kontsentratsii primesi. Togda v zavisimosti ot velichiny magnitnogo polya i kontsentratsii primesi voznikaet slozhnaya fazovaya diagramma razlichnykh magnitnykh sostoyanii 2DEG, vklyuchaya poyavlenie prostranstvennoi skirmionnoi tekstury, zadavaemoi raspredeleniem primesei v dvumernom kanale. Obsuzhdayutsya vozmozhnosti eksperimental’noi diagnostiki poluchennykh rezul’tatov.

Munchhausen effect: tunneling in an asymmetric SQUID

10 January 2008 in 11:30

V. Geshkenbein

A classical system cannot escape out of a metastable state at zero temperature. However, a composite system made from both classical and quantum degrees of freedom may drag itself out of the metastable state by a sequential process. The tunneling of the quantum degree of freedom entails a distortion in the trapping potential of the classical junction, which might be sufficiently large to transform the metastable state into an unstable one. The classical component then escapes. Such a situation can be conveniently studied and implemented in a dynamically asymmetric dc SQUID with two Josephson junctions of equal critical current Ic but strongly different shunt capacities C and/or shunt resistances R. We determine the dynamical phase diagram of this SQUID for various choices of junction parameters.

Effekt Kerra v sverkhprovodnikakh so spontannoi namagnichennost’yu

27 December 2007 in 11:30

V.P. Mineev

Naidena velichina vrashcheniya napravleniya polyarizatsii sveta (effekt Kerra) pri otrazhenii ot poverkhnosti sverkhprovodnika so spontannoi namagnichennost’yu. Rezul’taty obsuzhdayutsya v svyazi s nedavnimi nablyudeniyami effekta v sverkhprovodyashchem Sr2RuO4.

Interplay of coulomb and electron-phonon interactions in graphene

27 December 2007 in 11:30

Denis Basko (SISSA, Trieste)

 Electron-phonon coupling in graphene is currently a subject of intense research. Theoretically, the coupling constants are usually calculated using density-functional theory (DFT), where the exchange (Fock) term is treated in the local density approximation, or the generalized gradient approximation.
 In this work we consider mutual effect of weak electron-phonon and strong Coulomb interactions on each other by summing up leading logarithmic corrections via the renormalization group approach. We find that coupling constants to different phonon modes are renormalized differently, which explains the experimentally observed intensities of Raman peaks.

Provodimost’ dvumernykh sistem pri umen’shenii kF*l. Rol’ vzaimodeistviya i interferentsii. Perekhod k pryzhkovoi provodimosti

6 December 2007 in 11:30

G.M. Min’kov, A.A. Sherstobitov, A.V. Germanenko, O.E. Rut

Obsuzhdayutsya rezul’taty eksperimental’nykh issledovanii provodimosti dvumernykh sistem pri umen’shenii k_F*l:vozmozhnost’ razdeleniya vkladov v provodimost’ ot elektron-elektronnogo vzaimodeistviya, ot interferentsii i ikh sootnoshenie; diapazon provodimostei, v kotorom magnitopolevye i temperaturnye zavisimosti provodimosti, a takzhe neomicheskaya provodimost’ adekvatno opisyvayutsya v ramkakh modeli provodimosti po delokalizovannym sostoyaniyam obsuzhdayutsya kachestvennye otlichiya diffuzionnoi i pryzhkovoi provodimostei; perekhod k pryzhkovoi provodimosti i osobennosti pryzhkovoi provodimosti po sostoyaniyam, lokalizovannym za schet interferentsii. Pokazano, chto vklad elektron-elektronnogo vzaimodeistviya v provodimost’ sushchestvenno umen’shaetsya pri k_F*l3.
Interferentsionnaya popravka:
pri sigma=(10-2)*e2/h (chto sootvetstvuet 2< k_F*l

Perenos energii i strukturnye transformatsii v nelineinykh mekhanicheskikh tsepyakh i polimernykh kristallakh

22 November 2007 in 11:30

L.I. Manevich, E.A. Zubova (IKhF im. N.N. Semenova RAN)

Rassmatrivayutsya nelineinye kvaziodnomernye modeli, otrazhayushchie eksperimental’no nablyudaemye perenos energii i strukturnye transformatsii v mekhanicheskikh i polimernykh sistemakh. V pervoi chasti doklada pokazano, chto adekvatnoe opisanie perenosa i lokalizatsii energii v mekhanicheskikh sistemakh dostigaetsya pri vvedenii predel’nykh fazovykh traektorii, sostavlyayushchikh, v opredelennom smysle, al’ternativu nelineinym normal’nym modam. Takie spetsial’nye traektorii sootvetstvuyut polnomu energoobmenu mezhdu ostsillyatorami ili ostsillyatornymi tsepyami. Formuliruyutsya usloviya dinamicheskogo perekhoda «obmen-lokalizatsiya». Predlagaemyi podkhod illyustriruetsya na primere dvukh slabo svyazannykh ostsillyatorov. Zatem obsuzhdaetsya ego obobshchenie na sistemy s bol’shim chislom stepenei svobody, slabo svyazannye ostsillyatornye tsepi i osobyi klass sistem, v kotorykh prostranstvennaya odnorodnost’ narushena (tsep’ lineinykh ostsillyatorov s sil’no nelineinymi elementami). Modeli takogo roda voznikayut, v chastnosti, pri raschete energeticheskikh lovushek, sposobnykh zashchitit’ elementy konstruktsii ot intensivnogo impul’snogo vozdeistviya. Provedeno sopostavlenie analiticheskikh rezul’tatov s eksperimental’nymi dannymi, poluchennymi na model’noi sisteme. Vo vtoroi chasti doklada rassmotreny kvaziodnomernye analiticheskie i sil’no nizotropnye trekhmernye molekulyarno-dinamicheskie modeli, primenimye pri analize tverdykh polimerov, v otlichie ot kristallov nizkomolekulyarnykh veshchestv. Obsuzhdayutsya spetsificheskie dlya polimerov lokalizovannye kvaziodnomernye strukturnye defekty i nelineinye vozbuzhdeniya. Pokazano, chto ryad fizicheskikh protsessov v polimerakh (diffuziya tsepei i relaksatsiya v kristallitakh, mul’tistadiinye strukturnye transformatsii polimernykh kristallov v oblasti predplavleniya) proiskhodyat pri opredelyayushchem uchastii takikh nelineinykh vozbuzhdenii. Poluchennye analiticheskie i chislennye rezul’taty obsuzhdayutsya v svyazi s imeyushchimisya eksperimental’nymi dannymi.

Statfizika dionov i konfainment

25 October 2007 in 11:30

D.I. D’yakonov (PIYaF RAN)

V teorii Yanga-Millsa nedavno obnaruzheny novye klassicheskie resheniya, obobshchayushchie standartnye instantony takim obrazom, chto polyakovskaya petlya (golonomiya) mozhet prinimat’ lyubye znacheniya; novye instantony «sostoyat» iz N monopolei dlya kalibrovochnoi gruppy SU(N). Vychisleny kvantovyi determinant malykh fluktuatsii vokrug novykh instantonov, a takzhe mera integrirovaniya po ikh kollektivnym koordinatam. Takim obrazom, v kvaziklassicheskom priblizhenii statsumma teorii Yanga-Millsa priobretaet vid statsummy dlya ansamblya vzaimodeistvuyushchikh monopolei. V svoyu ochered’, eta statsumma tozhdestvenno perepisyvaetsya kak 3-mernaya kvantovaya teoriya polya, v kotoroi lyuboi korrelyator vychislyaetsya tochno, nesmotrya na vzaimodeistvie. V chastnosti, okazyvaetsya, chto mezhdu dvumya tyazhyolymi istochnikami (kvarkami) natyagivaetsya struna s vychislimym profilem i natyazheniem, prichyom natyazheniya strun dlya raznykh kalibrovochnykh grupp s vysokoi tochnost’yu sovpadayut s temi, chto byli polucheny pri komp’yuternom modelirovanii teorii Yanga-Millsa na reshyotke. Pri temperature vyshe nekotoroi kriticheskoi (takzhe sovpadayushchei dlya raznykh grupp s izmerennoi na reshyotke) ansambl’ monopolei perestraivaetsya, i proiskhodit dekonfainment.

Turbulentnost’ v akkretsionnykh diskakh

4 October 2007 in 11:30

A.M. Fridman

Iz pervykh printsipov poluchen koeffitsient turbulentnoi vyazkosti i spektr turbulentnosti v akkretsionnykh diskakh.

Non-Abelian strings and monopoles in supersymmetric gauge theories

27 September 2007 in 11:30

Alexei Yung (PIYaF)

We review progress made in understanding the mechanism of non-Abelian confinement in supersymmetric gauge theories. In particular, we discuss construction of non-Abelian flux tubes (strings) in N=2 supersymmetric QCD. In certain regimes Z_N Abelian strings acquire orientational zero modes associated with rotation of their color flux inside a non-Abelian subgroup of the gauge group. This make these strings genuinely non-Abelian. For bulk theories with U(N) gauge group the internal dynamics of non-Abelian strings is described in terms of two dimensional CP(N-1) model. Next we focus on the notion of non-Abelian monopole. In particular, we discuss non-Abelian monopoles confined by non-Abelian strings. In the world sheet theory on the string they appear as CP(N-1) model kinks.

Kogomologii dukhov i neperturbativnaya dinamika superstrun

13 September 2007 in 11:30

Dmitrii Polyakov

Formalizm dukhovykh kogomologii - perspektivnyi podkhod k izucheniyu neperturbativnoi dinamiki strun i kalibrovochnykh teorii. Etot formalizm pozvolyaet issledovat’ neperturbativnye effekty v etikh teoriyakh, tekhnicheski ne vykhodya za ramki teorii vozmushchenii. Glavnaya ideya etogo podkhoda v tom, chto informatsiya o neperturbativnoi dinamike teorii s lokal’nymi kalibrovochnymi simmetriyami soderzhitsya v osobom sektore ikh prostranstv sostoyanii, v kotorom materiya smeshana s dukhovymi stepenyami svobody. Obychno etot sektor sostoit iz lokal’nykh fizicheskikh operatorov, ne obladayushchikh yavnoi kalibrovochnoi simmetriei, no BRST-invariantnykh blagodarya ikh netrivial’nomu vzaimodeistviyu s dukhami. V chastnosti, perturbativnye korrelyatsionnye funktsii etikh osobykh operatorov vosproizvodyat neperturbativnuyu dinamiku strun i kalibrovochnykh teorii. Ispol’zuya etot formalizm, my izuchaem vozniknovenie skrytykh izmerenii v teorii superstrun i dvumernoi supergravitatsii, dinamiku superstrun v iskrivlennom prostranstve-vremeni i novye golograficheskie sootnosheniya mezhdu strunami i drugimi fizicheskimi teoriyami v razlichnykh izmereniyakh.

Anomal’naya spinovaya relaksatsiya v nanotrubkakh

6 September 2007 in 11:30

D.V. Bulaev (Bazel’skii universitet, Bazel’, Shveitsariya)

Doklad posvyashchyon teoreticheskomu issledovaniyu vremyon spinovoi relaksatsii i dekogerentsii v nanotrubkakh, kotorye proyavlyayut neobychnye svoistva v zavisimosti ot magnitnogo polya: 1) vremya spinovoi relaksatsii stremitsya k nulyu s umen’sheniem rasstoyaniya mezhdu urovnyami s protivopolozhnoi orientatsiei spina; 2) s uvelicheniem etogo rasstoyaniya obshchee povedenie vremeni relaksatsii stremitsya k uvelicheniyu; 3) vsledstvie interferentsionnykh effektov vremya spinovoi relaksatsii ostsilliruet kak funktsiya magnitnogo polya; 4) pri opredelyonnykh magnitnykh polyakh, v rezul’tate destruktivnoi interferentsii mezhdu razlichnymi vkladami v spinovuyu relaksatsiyu, proiskhodit rezkoe uvelichenie vremeni relaksatsii do 200 s.

Nelineinoe ushirenie spektra generatsii volokonnogo VKR-lazera (VKR - vynuzhdennoe kombinatsionnoe rasseyanie)

21 June 2007 in 11:30

Dokladchik: E.V. Podivilov (IAiE SO RAN, g. Novosibirsk) Soavtory: S.A. Babin, A.E. Ismagulov, S.I. Kablukov, D.V. Churkin

Deformirovannyi vignerovskii kristall v odnomernoi kvantovoi tochke

31 May 2007 in 11:30

Ya.V. Gindikin, V.A. Sablikov (IRE RAN)

Rabota posvyashchena sil’no korrelirovannomu sostoyaniyu elektronov v ogranichennoi odnomernoi sisteme. Dlya ego opisaniya provedeny detal’nye issledovaniya funktsii raspredeleniya elektronov po odnochastichnym sostoyaniyam i Fur’e-spektra prostranstvennogo raspredeleniya elektronnoi plotnosti. Ustanovleno, chto eti velichiny obladayut universal’nymi (ne zavisyashchimi ot potentsiala vzaimodeistviya i razmerov sistemy) osobennostyami, kotorye kharakterizuyut uporyadochenie elektronov i deformatsiyu vignerovskogo kristalla, obuslovlennuyu nalichiem granits. Funktsiya raspredeleniya imeet del’ta-obraznuyu osobennost’ na fermievskom impul’se, a Fur’e-spektr plotnosti imeet osobennost’ v vide stupen’ki na udvoennom fermievskom impul’se, tak chto Fur’e-garmoniki s volnovym vetrom bol’she etoi velichiny otsutstvuyut ili ischezayushche maly. Rabota provedena s ispol’zovaniem raznykh podkhodov. Metodom tochnoi diagonalizatsii naidena mnogochastichnaya volnovaya funktsiya, s pomoshch’yu kotoroi polucheny funktsiya raspredeleniya po odnochastichnym sostoyaniyam i Fur’e-spektr plotnosti, obladayushchie ukazannymi vyshe osobennostyami. Rezul’taty sopostavleny s izvestnymi v literature raschetami v ramkakh modeli lattindzherovoi zhidkosti. Okazalos’, chto eta model’ takzhe privodit k singulyarnostyam funktsii raspredeleniya i Fur’e-spektra plotnosti, no ikh forma nepravil’naya. S pomoshch’yu prostoi modeli vyyasneno, chto naidennye metodom tochnoi diagonalizatsii osobennosti svyazany s vignerovskim uporyadocheniem elektronov i deformatsiei vignerovskogo kristalla vsledstvie nalichiya granits, a oshibka v modeli lattindzherovoi zhidkosti obuslovlena tem, chto v nei narushaetsya polnaya neitral’nost’ sistemy, vsledstvie chego deformatsiya okazyvaetsya pereotsenennoi. Predlozhen podkhod, pozvolyayushchii v ramkakh metoda bozonizatsii pravil’no opisat’ korrelirovannoe sostoyanie. On osnovan na ispol’zovanii ispravlennogo vyrazheniya dlya bozonizovannogo operatora plotnosti, kotoryi ne narushaet sokhraneniya polnogo chisla chastits i neitral’nosti sistemy.

Phase structure of an abelian two-higgs model and high temperature superconductors

17 May 2007 in 11:30

Maxim Chernodub (ITEP)

Effekt mayatnika kapitsy v amorfnykh magnetikakh i sverkhtekuchem 3He v aerogele

26 April 2007 in 11:30

I.A. Fomin (IFP im. P.L. Kapitsy RAN)

V svyazi s identifikatsiei sverkhtekuchikh faz 3Ne v aerogele vnov’ rassmotren vopros o vliyanii slabogo vmorozhennogo besporyadka na vid i orientatsiyu parametra poryadka nepreryvno vyrozhdennykh sistem. Pokazano, v chastnosti, chto imeetsya klass "orbital’no izotropnykh" parametrov poryadka, dlya kotorykh besporyadok tipa "sluchainaya anizotropiya" ne privodit k razrusheniyu dal’nego poryadka po stsenariyu Larkina i Imri i Ma. Pokazano takzhe, chto v sluchae, kogda poluchennyi minimizatsiei svobodnoi energii parametr poryadka ne prinadlezhit k etomu klassu, imeetsya mekhanizm, kotoryi stremitsya izmenit’ vid parametra poryadka tak, chtoby sdelat’ ego bolee "izotropnym". Mekhanizm etot analogichen deistviyu vibratsii tochki podvesa na orientatsiyu mayatnika Kapitsy. Predlozhena struktura parametra poryadka A-podobnoi fazy 3Ne v aerogele, uchityvayushchaya "effekt mayatnika Kapitsy" i obsuzhdaetsya, v kakoi mere sushchestvuyushchie eksperimental’nye dannye soglasuyutsya s etoi strukturoi. V kachestve dal’neishego primera rassmotren amorfnyi ferromagnetik i pokazano, chto anizotropnyi besporyadok privodit k orientatsii parametra poryadka, prichem ego orientiruyushchee deistvie dostatochno sil’no dlya togo chtoby podavit’ effekt Larkina i Imri i Ma.

Spinovye kubity na osnove kvantovykh tochek v poluprovodnikakh III-V i grafene

19 April 2007 in 11:30

D.V. Bulaev (Bazel’skii universitet, Bazel’, Shveitsariya)

Pervaya chast’ doklada posvyashchena vremeni spinovoi relaksatsii i dekogerentsii elektronov i dyrok v dvumernykh kvantovykh tochkakh GaAs/InAs [D.V. Bulaev, D. Loss, Phys. Rev. B 71, 205324 (2005); Phys. Rev. Lett. 95, 076805 (2005)]. Budet proveden sravnitel’nyi analiz razlichnykh mekhanizmov spin-orbital’nogo vzaimodeistviya, predlozhen metod po eksperimental’nomu izmereniyu spin-orbital’nykh konstant Bychkova-Rashby i Dressel’khausa, issledovana nemonotonnaya zavisimost’ vremeni spinovoi relaksatsii ot velichiny magnitnogo polya i obsuzhdena realizatsiya kvantovykh tochek, v kotorykh vremya spinovoi relaksatsii tyazhelykh dyrok mozhet prevyshat’ sootvetstvuyushchee vremya dlya elektronov. Vo vtoroi chasti doklada obsuzhdaetsya metod polucheniya kvantovykh tochek na osnove monosloya grafena [B. Trauzettel, D.V. Bulaev, D. Loss, G. Burkard, Nature Physics 3, 192 (2007)]. Budut issledovany unikal’nye svoistva elektronov v grafenovykh kvantovykh tochkakh, kotorye otkryvayut vozmozhnost’ k sil’nomu vzaimodeistviyu udalennykh kvantovykh tochek, chto printsipial’no ne dostizhimo v obychnykh poluprovodnikovykh strukturakh i yavlyaetsya vazhnym elementom realizatsii otkazoustoichivykh (fault-tolerant) kvantovykh vychislenii.

Neravnovesnye yavleniya v uzkikh sverkhprovodyashchikh plenkakh nbn pri pogloshchenii ik fotona

5 April 2007 in 11:30

G.N. Gol’tsman (Moskovskii pedagogicheskii gosudarstvennyi universitet)

Issleduetsya neravnovesnoe sostoyanie, voznikayushchee v uzkikh poloskakh iz tonkikh plenok gryaznykh sverkhprovodnikov pri pogloshchenii IK fotona. Obnaruzheno vozniknovenie rezistivnosti i korotkogo impul’sa napryazheniya, kogda poloska podderzhivaetsya pri temperature sushchestvenno nizhe kriticheskoi temperatury perekhoda i neset transportnyi tok blizkii k kriticheskomu. Predlozhena fenomenologicheskaya model’, ob’yasnyayushchaya vozniknovenie rezistivnosti obrazovaniem «goryachego pyatna» neravnovesnykh kvazichastits v meste pogloshcheniya fotona i posleduyushchim vytesneniem sverkhtoka iz etoi oblasti. Na osnove obnaruzhennykh neravnovesnykh effektov byli sozdany bystrodeistvuyushchie i vysokochuvstvitel’nye odnofotonnye detektory IK diapazona, a takzhe bolometry i smesiteli millimetrovogo i submillimetrovogo diapazonov voln.

Investigation of larkin-imry-ma effect: random anisotropy of aerogel destroys the long-range orientational order in superfluid 3He-A

22 March 2007 in 11:30

G.E. Volovik

We discuss recent NMR experiments on superfluid 3He-A confined in aerogel. Silicon strands of aerogel play the role of impurities with quenched random anisotropy. We present experimental evidences of Larkin-Imry-Ma effect: randomly oriented silicon strands destroy the long-range orientational order in 3He-A. The long-range orientational order is restored when a small regular anisotropy is applied either by uniaxial deformation of aerogel or by external superfluid current. There are many open problems which require further experimental and theoretical efforts, such as the role of the topological defects and whether the superfluidity is suppressed by the Larkin-Imry-Ma effect.

Perekhod metall-izolyator v dvumernoi sil’no-korrelirovannoi elektronnoi sisteme. Sopostavlenie eksperimental’nykh dannykh s dvukhparametricheskoi skeilingovoi teoriei finkel’shteina

15 March 2007 in 11:30

D.A. Knyazev, O.E. Omel’yanovskii, V.M. Pudalov (FIAN), I.S. Burmistrov, N.M. Shchelkachev (ITF)

V doklade budet predstavlen obzor eksperimental’nykh dannykh po zavisimosti soprotivleniya dvumernoi elektronnoi sistemy v Si-MOSFET strukturakh ot temperatury (T) i parallel’nogo magnitnogo polya (B). Parametrami dvukhparametricheskoi skeilingovoi teorii i koordinatami fazovoi RG-diagrammy yavlyayutsya besporyadok i vzaimodeistvie, a tekushchei peremennoi - kvantovaya dlina. V to vremya kak neposredstvenno izmeryaemoe v eksperimente soprotivlenie yavlyaetsya neplokhim predstavleniem besporyadka, a dlina dostatochno nadezhno svyazyvaetsya s temperaturoi, izvlechenie iz eksperimenta parametra vzaimodeistviya γ2 v trebuemoi oblasti temperatur predstavlyaet trudnosti. V doklade budut rassmotreny popytki eksperimental’nogo opredeleniya temperaturnoi zavisimosti parametra vzaimodeistviya γ2 i ego sopostavlenie s RG teoriei. V chastnosti, budut predstavleny nedavnie rezul’taty po samosoglasovannomu opredeleniyu γ2(T) iz izmerenii temperaturnoi zavisimosti magnitosoprotivleniya R(T,B) v parallel’nom magnitnom pole vblizi perekhoda so storony metallicheskoi fazy. Budut privedeny rezul’taty analiza eksperimental’nykh zavisimostei R(T) v kriticheskoi oblasti, kotorye podtverzhdayut dvukhparametricheskii kharakter skeilinga.

How to measure a fractional statistical phase

22 February 2007 in 11:30

Yuval Gefen (Weizmann Institute of Sciences)

One of the pillars of quantum mechanics is the (quantum) statistics of identical particles. In two-dimensions particles (anyons) whose statistics (hence statistical phase) is intermediate between bosons and fermions do exist. I will discuss proposals to measure their statistical phase.

Dal’nii poryadok i zhidkost’ Lattindzhera v kvaziodnomernykh provodnikakh

8 February 2007 in 11:30

S.N. Artemenko (Institut radiotekhniki i elektroniki RAN)

Izuchaetsya vozmozhnost’ dal’nego poryadka v sisteme vzaimodeistvuyushchikh elektronov s odnomernym spektrom, no nakhodyashchikhsya v 3D prostranstve i poetomu vzaimodeistvuyushchikh s 3D ob’ektami. Pokazano, chto v sluchae mezhelektronnogo ottalkivaniya slaboe vzaimodeistvie elektronov s 3D fononami mozhet stabilizirovat’ dal’nii poryadok volny zaryadovoi plotnosti (VZP) v poluprovodnikovykh kvantovykh provolokakh (ikh tipichnaya tolshchina velika po sravneniyu s mezhatomnymi rasstoyaniyami - neskol’ko desyatkov nanometrov), a takzhe v kvaziodnomernykh kristallakh s tsepochechnoi strukturoi. Sostoyanie s VZP v takoi sisteme opisyvaetsya na osnove kontseptsii zhidkosti Lattindzhera, podobno tomu, kak klassicheskoe reshenie zadachi Paierlsa osnovano na predstavleniyakh fermi-zhidkosti. V sluchae odinochnoi metallicheskoi tsepochki vzaimodeistviya s 3D fononami podlozhki okazyvaetsya nedostatochno dlya stabilizatsii dal’nego poryadka i trebuetsya narushenie prostranstvennoi invariantnosti za schet defektov ili soizmerimosti. Rassmotrena takzhe sistema elektronov s prityazheniem i pokazano, chto v etom sluchae mozhet byt’ stabilizirovan sverkhprovodyashchii dal’nii poryadok za schet tunnel’nogo kontakta s 3D metallom.

Tochno reshaemaya model’ Tomonagi-Lattinzhera s nelineinoi dispersiei

25 January 2007 in 11:30

A.V. Rozhkov (Institut teoreticheskoi i prikladnoi elektrodinamiki RAN)

V rabote issleduetsya model’ odnomernykh vzaimodeistvuyushchikh besspinovykh elektronov Tomonagi-Lattinzhera. Pokazano, chto sushchestvuet unitarnyi operator, kotoryi preobrazuet sistemu Tomonagi-Lattinzhera v sistemu slabo vzaimodeistvuyushchikh fermionnykh kvazichastits. Dannoe kanonicheskoe preobrazovanie ustranyaet iz gamil’toniana operator mezhelektronnogo vzaimodeistviya, yavlyayushchiisya marginal’nym v smysle teorii renormalizatsionnoi gruppy. Ostavshiesya operatory vzaimodeistviya mezhdu kvazichastitsami yavlyayutsya nerelevantnymi. Predlozhennaya tekhnika mozhet byt’ primenena dlya issledovaniya svoistv odnomernykh fermionov s nelineinoi dispersiei, zameshchaya traditsionnuyu dlya odnomernykh sistem bozonizatsiyu, kotoraya ispytyvaet ser’eznye slozhnosti v tekh sluchayakh, kogda neobkhodim uchet nelineinoi dispersii. My prodemonstriruem, chto pri soblyudenii nekotorogo usloviya, nalagaemogo na parametry modeli, rassmotrennoe unitarnoe preobrazovanie otobrazit gamil’tonian Tomonagi-Lattinzhera na gamil’tonian svobodnykh kvazichastits. V takom sluchae model’ reshaetsya tochno, chto daet vozmozhnost’ vychislit’ propagator plotnost’-plotnost’.

Carbon nanotube superconducting quantum interference device

21 December 2006 in 11:30

V. Bouchiat (CNRS Grenoble)

Recent progress in improving the contact of single-walled carbon nanotubes (SWNTs) to superconducting nanoelectrodes showed that such molecules can accommodate a superconducting current and behave as gate-controlled Josephson junctions. Such carbon nanotube (CNT) junctions allow to implement a new type of weak link that can be coupled quantum dots reminiscent to the well studied superconducting single-electron transistor but with the added presence of strong quantum confinement. We report on the study of a superconducting quantum interference device (SQUID) with SWNTs Josephson junctions. Quantum confinement in each junction induces a discrete quantum dot (QD) energy level structure, which can be controlled with two lateral electrostatic gates. In addition, a backgate electrode can vary the transparency of the QD barriers, thus permitting to change the hybridization of the QD states with the superconducting contacts. The gates are also used to directly tune the quantum phase interference of the Cooper pairs circulating in the SQUID ring. Optimal modulation of the switching current with magnetic flux is achieved when both QD junctions are in the “on” or “off” state. In particular, the SQUID design establishes that these CNT Josephson junctions can be used as gate-controlled π-junctions, that is, the sign of the current-phase relation across the CNT junctions can be tuned with a gate voltage. The CNT-SQUIDs provide a new generation of ultra-sensitive magnetometers of nanometer-sized samples, which are very promising to study the magnetisation reversal of an individual magnetic particle or molecule placed on one of the two carbon nanotube Josephson junctions. Such devices offer also the opportunity to test interesting physical phenomena ranging from Kondo physics to π-junctions and pave the way for non-locality experiments by generating pairs of entangled electrons in a nanotube.

Bioinformatika: kak zanimat’sya molekulyarnoi biologiei, ne imeya nichego, krome komp’yutera i interneta

14 December 2006 in 11:30

M.S. Gel’fand (Uchebno-nauchnyi tsentr, Institut problem peredachi informatsii)

Sovremennaya molekulyarnaya biologiya perezhivaet smenu epokh. Poyavlenie industrial’nykh metodov sekvenirovaniya genomov (opredeleniya posledovatel’nosti DNK), opredeleniya urovnya ekspressii (intensivnosti raboty) genov, analiza belok-DNKovykh i belok-belkovykh vzaimodeistvii i t.p. privelo k tomu, chto ob’em dannykh sushchestvenno prevoskhodit vozmozhnost’ ikh osmysleniya bez primeneniya komp’yuternogo analiza. V rezul’tate poyavilas’ novaya oblast’ nauchnoi deyatel’nosti - bioinformatika, kotoraya analiziruet i sopostavlyaet eti dannye i delaet na etoi osnove biologicheski osmyslennye utverzhdeniya. Ya poprobuyu rasskazat’ pro nekotorye osnovnye priemy, kotorye ispol’zuyutsya dlya analiza genomov, kartirovaniya genov i predskazaniya ikh funktsii i regulyatsii, i pokazat’ kak oni rabotayut v real’noi praktike. Obshchii plan doklada primerno takov: biologicheskii likbez s vvedeniem osnovnykh terminov i ponyatii zadacha kartirovaniya genov sravnitel’naya genomika i funktsional’naya annotatsiya genov (sluchai iz zhizni) desert na vybor: predvaritel’nye nablyudeniya pro evolyutsiyu regulyatornykh sistem ili poverkhnostnyi obzor chuzhikh rabot po sistemnoi biologii (obshchie svoistva grafov, voznikayushchikh v razlichnykh molekulyarno-biologicheskikh zadachakh).

Universal and non-universal tails of free energy distribution function in the random directed polymer problem

7 December 2006 in 11:30

I.V. Kolokolov, S.E. Korshunov

A modification of the optimal fluctuation approach is applied to study the tails of the free energy distribution function P_L(F) for an elastic string in random media both in the regions of the universal behavior of P_L(F) and in the regions of large fluctuations, where the behavior of P_L(F) deviates from universal. The difference between the two regimes is shown to consist in whether it is necessary or not to take into account the renormalization of parameters by fluctuations of disorder in the vicinity of the optimal fluctuation.

Elektronnaya struktura vikhrevykh klasterov v sverkhprovodnikakh vtorogo roda

30 November 2006 in 11:30

A. Mel’nikov (Institut fiziki mikrostruktur RAN, N. Novgorod)

Issledovana elektronnaya struktura vikhrevykh konfiguratsii v cverkhprovodnikakh vtorogo roda s uchetom tunnelirovaniya kvazichastits mezhdu vikhryami. Tunnelirovanie privodit k sil’noi gibridizatsii sostoyanii, lokalizovannykh na sosednikh vikhryakh, kogda rasstoyanie mezhdu nimi a<ac, gde kriticheskoe rasstoyanie ac poryadka neskol’kikh dlin kogerentnosti. Dlya vikhrevykh klasterov, svyazannykh kvazichastichnym tunnelirovaniem, naiden stsenarii perekhoda ot vyrozhdennogo spektra Karoli - de Zhena - Matrikona k spektru mnogokvantovykh vikhrei. Transformatsiya spektra privodit k poyavleniyu plotnosti sostoyanii na urovne Fermi, kotoraya ostsilliruet kak funktsiya rasstoyaniya a. Obsuzhdaemye effekty mogut nablyudat’sya v mezoskopicheskikh sverkhprovodnikakh, a takzhe v neuporyadochennykh vikhrevykh konfiguratsiyakh v makroskopicheskikh sistemakh. Dlya sluchaya vikhrei v mezoskopicheskikh sverkhprovodnikakh izuchena takzhe modifikatsiya spektra kvazichastits s uchetom normal’nogo rasseyaniya na granitsakh obraztsa. Pokazano, chto rassmotrennye effekty tunnelirovaniya kvazichastits mezhdu vikhryami i rasseyanie na granitse privodyat k sushchestvennomu uvelicheniyu chisla kvazichastichnykh mod, rasprostranyayushchikhsya vdol’ vikhrevykh linii i opredelyayushchikh, v chastnosti, teploprovodnost’ obraztsa.

Anomal’noe magnitosoprotivlenie 2D sistem, obuslovlennoe nemarkovskimi effektami

16 November 2006 in 11:30

V. Kachorovskii (FTI im. Ioffe, S.-Peterburg)

O vozmozhnosti tripletnoi sverkhprovodimosti v NaCoO2 i SrRuO3

19 October 2006 in 11:30

I.I. Mazin

Netrivial’naya dinamika v dvumernykh gamil’tonovykh sistemakh

28 September 2006 in 11:30

P.G. Grinevich

«Naivnaya» tochka zreniya sostoit v tom, chto gamil’tonovy sistemy s dvumya stepenyami svobody trivial’ny, poskol’ku dvizhenie proiskhodit po liniyam urovnya gamil’toniana. Odnako esli sam gamil’tonian — kvaziperiodicheskaya funktsiya, to topologiya linii urovnya, i kak sledstvie, dinamika stanovyatsya ochen’ slozhnymi. Vazhnyi primer — kvaziklassicheskoe dvizhenie elektrona v dostatochno sil’nykh magnitnykh polyakh pri nizkikh temperaturakh, izuchavsheesya v rabotakh khar’kovskoi shkoly: (Lifshits, Asbel’, Kaganov, Peschanskii). Topologiya traektorii byla issledovana v rabotakh Novikova i ego uchenikov (Zorich, Dynnikov, Tsarev, Mal’tsev i dr). Svyaz’ s nizkotemperaturnoi provodimost’yu issledovana v nedavnikh rabotakh Novikova i Mal’tseva. Drugoi primer, dostatochno blizkii k pervomu — gamil’tonovy potoki na rimanovykh poverkhnostyakh s pochti vsyudu ploskoi metrikoi. Esli vybrat’ krivuyu na poverkhnosti, nigde ne kasayushchuyusya potoku, to gamil’tonova dinamika mozhet byt’ perekodirovana v otobrazhenie perekladyvaniya otrezka — odnu ikh bazisnykh modelei statfiziki. Okazyvaetsya, chto svoistva otobrazheniya perekladyvaniya otrezka mozhno issledovat’ s pomoshch’yu teorii rimanovykh poverkhnostei (potoki na prostranstve modulei) (Masur, Veech, Zorich, Kontsevich). V kontse budet rasskazano o nedavnem nablyudenii avtora i Paolo Maria Santini. Rassmotrim nelineinyi ostsillyator x″ = − x2n+1. Esli sleduya F. Calogero vvesti kompleksnoe vremya i rassmotret’ dvizhenie po okruzhnosti v ploskosti kompleksnogo vremeni, to sootvetstvuyushchaya dinamika chisto periodichna dlya okruzhnostei dostatochno malogo radiusa, no pri uvelichenii radiusa iz-za vetvleniya reshenii povedenie sil’no uslozhnyaetsya. Komp’yuternye eksperimenty ukazyvayut na poyavlenie khaoticheskikh rezhimov i fraktalov na mnozhestve nachal’nykh uslovii.

Krupno-masshtabnaya kogerentnost’ boze-kondensata dipolyarnykh eksitonov

7 September 2006 in 11:30

V.B. Timofeev (IFTT)

Recent discoveries in quasi one dimentional conductors as an access to physics of solitons

22 June 2006 in 11:30

Serguei Brazovskii

This talk will firstly review two recent discoveries done by scientists of the IRE RAN (Latyshev, Nad, et al) in collaboration at Grenoble (Monceau et al), Orsay (S.B.) and ITP RAN (Matveenko, S.B.). The first one (F.Ya. Nad et al) is the observation of the Ferroelectric transition coupled with the charge disproportionation in organic conductors. The state gives rise to three types of solitons: pi- solitons (holons) are observed in conductivity and optics; fractionally charged solitons are seen as ferroelectric domain walls via the frequency dispersion of the electric response; topologically coupled combined spin-charge solitons appear below occasional subsequent structural transitions. The second discovery (Yu.I. Latyshev et al) is based on the new techniques of the internal coherent tunneling within nanoscale mesa-junctions, which was applied to compounds with Charge Density Waves. The experiments give a direct access to observations of two types of solitons in dynamics, as well as of their aggregated states in statics. Based on these experimental proves, we shall discuss possible generalizations for the role of microscopic topological objects. We shall construct a scheme of combined topological objects which may work in general types of strongly correlated systems.

Metod molekulyarnoi dinamiki: vklad v osnovaniya i prilozheniya statisticheskoi fiziki i fizicheskoi kinetiki

15 June 2006 in 11:30

G. Norman

Osobennosti mikrovolnovoi provodimosti kristallov vtsp s raznymi urovnyami dopirovaniya

8 June 2006 in 11:30

M.R. Trunin (IFTT RAN)

Results of recent investigations of the temperature dependences of the surface impedance Z(T) = R(T) + iX(T) and conductivity \sigma(T) in the ab-plane and along c-axis of high-Tc superconductors (HTSC) are discussed. The main attention is focused on the peculiarities of these dependences in single crystals of YBa2Cu3O7-x with the oxygen deficiency varied in the range 0.07 <= x <= 0.47 (92 >= Tc >= 41 K) and of Ba1-xKxBiO3 with different potassium content 0.6 >= x >= 0.35 (5 <= Tc <= 31 K).
An analysis of the resistivity \hat\rho(T) = 1 / \hat\sigma(T) tensor in the normal state indicates that the optimally doped YBa2Cu3O6.93 is a three-dimensional anisotropic metal. As the oxygen content is decreased, the Drude c-axis conductivity changes to the hopping one, the crossover occurring at \rho_c \rho_ab \approx 10-6 (Ohm∙cm)2. In the superconducting state of YBa2Cu3O7-x with x > 0.35 the behavior of the superfluid density n_s(T,x) \propto \sigma''_ab(T,x) can be treated in the framework of d-density wave (DDW) scenario of pseudogap in underdoped HTSC. The observed peculiarities of the imaginary part \sigma''_c(T,x) of the c-axis conductivity at T << Tc are determined by a strong decrease of the interlayer coupling integral with an increase of x.
Measurements of the surface impedance Z(T) in Ba1-xKxBiO3 crystals with Tc = 11 K (x \approx 0.5) and Tc = 30 K (x \approx 0.4) allow one to establish that the former is a BCS-superconductor (Z(T) saturates exponentially with lowering temperature at T << Tc) and the latter is not (Z(T) is linear at T << Tc). In addition, it is found that the temperature dependences of the upper critical field Hc2(T) of the crystals with Tc > 20 K are similar to those in HTSCs, both exhibiting strong positive curvature. On the contrary, Hc2(T) curves of the crystals with Tc < 15 K are in complete agreement with the BCS theory. The transition from BCS-type to HTSC-like superconductivity in Ba1-xKxBiO3 is interpreted within Abrikosov's extended saddle-point model.
The report is based on recent review articles [1,2] of the author and latest experimental results. [1] M.R. Trunin and A.A. Golubov. In-plane microwave response of high-Tc single crystals: Experiment and theory. in 'HTSC Spectroscopy', eds. N.M.Plakida, chapter 3, p.p.159-233 (Taylor and Francis, London and New York, 2003). [2] M.R. Trunin. Conductivity anisotropy and pseudogap in the microwave response of high-Tc superconductors. Physics-Uspekhi 48, 979 (2005).

Vozniknovenie za konechnoe vremya osobennosti u kompleksnykh reshenii uravneniya Nav’e-Stoksa i metod renorm-gruppy

1 June 2006 in 11:30

Ya.G. Sinai

V sovmestnoi rabote s Dong Li my pokazyvaem, chto dlya semeistva nachal’nykh dannykh uravneniya Nav’e-Stoksa, zavisyashchikh ot opredelennogo chisla parametrov, imeetsya nekotoryi nabor, pri kotorom za konechnoe vremya voznikaet osobennost’. Chislo etikh parametrov opredelyaetsya spektrom linearizatsii nepodvizhnoi tochki sootvetstvuyushchikh renorm-gruppovykh uravnenii.

Evolution of the head-tail patterning system in the fly

18 May 2006 in 11:30

Eric Siggia (Rockefeller University)

A central tenant of the emerging field of evolution and development is that most novelity arises from the redeployment of old genes in new contexts rather than the creation of entirely new genes. This view makes gene regulation an important force in evolution. The seminar will discuss the earliest patterning in the fly embryo and how it differs among related species of flies that diverged ~15-20 million years ago (a distance measured in molecular terms of twice the distance between human and mouse). I will show how campuational methods can predict regulation from genomic sequence and the molecular events that lead to step wise evolution of the genome.

Raschet iz 'pervykh printsipov' elektronnoi struktury sil’no-korrelirovannykh materialov

11 May 2006 in 11:30

Vladimir Anisimov (Institut fiziki metallov UrO RAN, Ekaterinburg)

Raschety elektronnoi struktury sil’no-korrelirovannykh materialov dolzhny yavno uchityvat’ kulonovskoe vzaimodeistvie mezhdu d- i f- elektronami. Na urovne priblizheniya staticheskogo srednego polya eto realizovano v metode LDA+U. Etot metod byl primenen dlya issledovaniya effektov zaryadovogo, spinovogo i orbital’nogo uporyadocheniya v razlichnykh soedineniyakh perekhodnykh metallov otnosyashchikhsya k klassu motovskikh izolyatorov. V doklade rassmatrivayutsya sleduyushchie primery:
Zaryadovoe uporyadochenie: Fe3O4;
Spinovoe uporyadochenie: raschet parametrov obmennykh vzaimodeistvii v CaVnO2n+1;
Orbital’noe uporyadochenie: KCuF3, LaMnO3;
Odnovremennoe zaryadovoe i orbital’noe uporyadochenie: Pr0.5Ca0.5MnO3;
Perekhody mezhdu nizko-spinovym i vysoko-spinovym sostoyaniyami: Co+3 v LaCoO3;
Polosovaya struktura v kupratakh;
Sil’no-korrelirovannye metally trebuyut ucheta dinamicheskikh effektov otsutstvuyushchikh v priblizhenii staticheskogo srednego polya i mogut issledovat’sya metodom LDA+DMFT osnovannym na teorii Dinamicheskogo Srednego polya.

Seminar v chetverg 20.04 ne sostoitsya. Ranee ob’yavlennyi doklad perenositsya na neopredelennyi srok v svyazi s bolezn’yu dokladchika

20 April 2006 in 11:30

Spinovaya dinamika elektronov v dvumernykh sistemakh

30 March 2006 in 11:30

M.M. Glazov (Fiziko-TekhnicheskiišInstitut im.šA.F. Ioffe RAN, S.-Peterburg)

Doklad posvyashchen spinovoi dinamike elektronov provodimosti v ob’emnykh poluprovodnikakh i poluprovodnikovykh strukturakh s kvantovymi yamami i provolokami iz netsentrosimmetrichnykh materialov. Osnovnoe vnimanie budet udeleno analizu spinovoi relaksatsii elektronnogo gaza v mekhanizme D’yakonova-Perelya.Plan doklada: mekhanizmy spinovoi relaksatsii v poluprovodnikakh; pretsessionnyi mekhanizm spinovoi relaksatsii (mekhanizm D’yakonova-Perelya); vliyanie elektron-elektronnykh stolknovenii na spinovuyu relaksatsiyu; integral stolknovenii dlya spinovoi matritsy plotnosti pri proizvol’noi stepeni vyrozhdeniya elektronnogo gaza; rol’ vzaimodeistviya v sluchae vysokoi spinovoi polyarizatsii elektronov; sopostavlenie teorii i eksperimental’nykh dannykh; zamedlenie spinovoi relaksatsii magnitnym polem; rol’ fluktuatsii konstanty spin-orbital’nogo vzaimodeistviya; neeksponentsial’naya relaksatsiya spina v sil’nom magnitnom pole.

Neabelevy struny i domennye stenki v supersimmetrichnoi teorii Yanga-Millsa

2 March 2006 in 11:30

A. Gorskii (ITEF)

Perestroika odnochastichnykh stepenei svobody v sil’nokorrelirovannykh Fermi-sistemakh

9 February 2006 in 11:30

V.A. Khodel’ (RNTs 'Kurchatovskii institut')

Time-dependent random matrices: quantum interference effects

12 January 2006 in 11:30

M.A. Skvortsov

 It is well established that the energy level statistics in disordered mesoscopic samples is universal and can be described by random matrices of an appropriate symmetry. The random matrix theory studied in great detail provides complete information about the spectral statistics. However, much less is known about time-dependent random matrices, which appear in studying, e.g., a quantum dot subject to a time-dependent gate voltage.
 We review recent progress in time-dependent random matrices. On a semiclassical limit, the energy absorption rate can be calculated with the help of the Kubo formula. Quantum phenomena modify this result. We show that there are two types of interference effects. The first effect is controlled by the velocity of the perturbation and is responsible for the transition between Kubo and Landau-Zener regimes of dissipation. The second effect is operative for time-reentrant perturbations when dynamic localization in the energy space may take place. We demonstrate that these effects can be described on the same footing within the Keldysh sigma-model formalism.

Ob uprugoi strune na sluchainom rel’efe

29 December 2005 in 11:30

I.V. Kolokolov

Vychislyayutsya asimptotiki funktsii raspredeleniya polozheniya kontsa uprugoi struny v dvumernom sluchainom potentsiale pri nizkikh, no konechnykh temperaturakh.

Nizkochastotnaya spinovaya dinamika v sil’nykh magnitnykh polyakh

8 December 2005 in 11:30

A.M. Farutin, V.I. Marchenko (IFP)

Sverkhprovodimost’ na poroge lokalizatsii v plenkakh TiN

1 December 2005 in 11:30

T.I. Baturina (IFP SO RAN, Novosibirsk)

Predstavleny eksperimental’nye rezul’taty po provodimosti tonkikh sverkhprovodyashchikh plenok TiN s razlichnoi stepen’yu besporyadka. Pokazano, chto analiz rezul’tatov dlya plenok s otnositel’no malym soprotivleniem mozhet byt’ uspeshno proveden na osnove teorii kvantovykh popravok Larkina-Galitskogo. Dlya bolee sil’no razuporyadochennykh plenok obnaruzheno universal’noe povedenie provodimosti v predele ochen’ sil’nykh magnitnykh polei i nulevoi temperatury: nasyshchenie soprotivleniya na velichine ravnoi kvantu soprotivleniya h/e2

Spontannoe parametricheskoe rasseyanie sveta

17 November 2005 in 11:30

A.N. Penin (MGU)

Protsess spontannogo parametricheskogo rasseyaniya sveta (SPR), ego priroda i osobennosti. Istoriya predskazaniya i nablyudeniya etogo printsipial’no kvantovogo yavleniya nelineinoi optiki. Vozmozhnye primeneniya SPR dlya spektroskopii fononov v kristallakh bez tsentra simmetrii (para- i segnetoelektrikakh). Primery izucheniya mnogochastichnykh fononnykh sostoyanii, proyavleniya rezonansa Fermi, izmeneniya kolebatel’nykh spektrov pri segnetoelektricheskikh i kontsentratsionnykh fazovykh perekhodakh. Problema analiza opticheskikh svoistv prostranstvenno-neodnorodnykh kristallov. Kvantovye kharakteristiki bifotonnogo polya, rozhdayushchegosya pri SPR i ikh ispol’zovanie dlya realizatsii metodov absolyutnoi fotometrii i sozdaniya polei s neklassicheskoi statistikoi.

Quantum phase transitions from topology in momentum space

3 November 2005 in 11:30

G. Volovik

Many quantum condensed-matter systems, and, probably, the quantum vacuum of Standard Model, are strongly correlated and strongly interacting fermionic systems, which cannot be treated perturbatively. However, physics which emerges in the low-energy corner does not depend on the complicated details of the system and is relatively simple. It is determined by the nodes in the fermionic spectrum, which are protected by topology in momentum space (in some cases, in combination with the vacuum symmetry). We illustrate this universality on some examples of quantum phase transitions, which can occur between the vacua with the same symmetry but with different topology of nodes in momentum space, such as Lifshitz transition in the case of the Fermi surfaces. The quantum phase transitions between the fully gapped states with the same symmetry but with different momentum-space topology (such as plateau-plateau transition in intrinsic QHE and quantum transition in 1D Ising model) are also discussed.

Metod diffuzionnogo Monte-Karlo v sistemakh mnogikh chastits

20 October 2005 in 11:30

G.E. Astrakharchik (Institut spektroskopii RAN i Universitet Trento, Italiya)

Femtosecond laser ablation

13 October 2005 in 11:30

S.I. Anisimov, N.A. Inogamov, V.A. Khokhlov, K. Nishihara, Yu.V. Petrov, V.V. Zhakhovskii

Theoretical, numerical, and experimental description of ultrashort (τl sim 30 - 300 fs) laser pulse action on metals and semiconductors is discussed. Duration of laser pulse τl is so short that during the pulse only electron subsystem absorbs laser energy. This separates physics of femtosecond pulses from cases with longer durations (several ps and more) when electron and ion subsystems are in mutual thermal equilibrium. Variation of matter reply to laser action is described in continuous wide interval of absorbed energy.

The primordial perturbation spectrum

29 September 2005 in 11:30

A.A. Starobinsky

Primordial scalar (adiabatic) perturbations and tensor ones (gravitational waves) are the main observable quantities which remained from very early stages of evolution of our Universe. Observational data show that the Fourier power spectrum of density perturbations is very close to the flat (i.e., the Harrison-Zeldovich) one and their statistics is Gaussian, in agreement with predictions of the simplest versions of the inflationary scenario of the early Universe. However, some small deviations from the flat spectrum and the Gaussian statistics are expected generically. I review recent theoretical and observational results on the primordial perturbation spectrum including a new general expression for the spectrum of adiabatic perturbations unifying different ways of their generation both during and after inflation, as well as two exact solution for inflaton field potentials producing a) the exactly flat adiabatic spectrum, b) the constant ratio of tensor/scalar perturbation power spectra.

Wave turbulence theory (WTT) for discrete systems

22 September 2005 in 11:30

Elena Kartashova

Classical WTT allows to approximate original nonlinear evolution equations by corresponding kinetic equations which are easier to study, to model numerically, to compute Kolmogorov's spectra for them, etc. It is well known that kinetic equations do not work in large scale wave systems (so-called finite-size effects in resonators), i.e. in systems with discrete spectra. We are going to present self-consistent theory of wave turbulence for these systems and illustrate it with examples for waves in water, ocean, atmosphere, plasma. Mathematical part of this theory is based on the general results and methods of number theory which are used to construct reductions of the original evolution nonlinear PDE to a few small systems of ODEs describing resonances of the wave system.

1/f noise and two-level systems in Josephson qubits

15 September 2005 in 11:30

A. Shnirman

Novyi malyi parametr i stepennoi ryad dlya 3-mernoi sistemy Nav’e-Stoksa vo vsem prostranstve

16 June 2005 in 11:30

Ya.G. Sinai

We consider the Fourier transform of the usual Navier-Stokes system on R3. Surprisingly enough, some simplification arises if one allows solutions with infinite energy and enstrophy. A new small parameter for such solutions can be introduces and a power series in powers of this parameter can be written. The solution can be represented as a sum of new diagrams which can be effectively estimated.

Blow-up in the nonlinear wave equation

9 June 2005 in 11:30

Yu.N. Ovchinnikov

Sverkhprovodimost’ vblizi perekhoda andersona i lokalizovannye pary

2 June 2005 in 11:30

M.V. Feigel’man

Budet predstavlen obzor osnovnykh eksperimental’nykh faktov po nizkotemperaturnomu povedeniyu sil’no neuporyadochennykh soedinenii (InO, TiN, sverkhtonkie metallicheskie plenki) vblizi perekhoda sverkhprovodnik-dielektrik i izlozhena polufenomenologicheskaya teoriya elektronnogo sparivaniya na lokalizovannykh sostoyaniyakh (po rezul’tatam, predstavlennym v preprinte M.Feigel'man, L.Ioffe, E.Yuzbashyan, cond-mat/0504766).

Analytical realization of finite-size scaling for Anderson localization: is there transition in the 2D case?

19 May 2005 in 11:30

I.M. Suslov (P.L. Kapitza Institute for Physical Problems)

Roughly half of numerical investigations of the Anderson transition are based on consideration of an associated quasi-1D system and postulation of one-parameter scaling for the minimal Lyapunov exponent. If this algorithm is taken seriously, it leads to unumbiguous prediction of the 2D phase transition. The transition is of the Kosterlitz-Thouless type and occurs between exponential and power law localization (Pichard and Sarma, 1981). This conclusion does not contradict numerical results if the raw data are considered. As for interpretation of these data in terms of one-parameter scaling, such interpretation is inadmissible: the minimal Lyapunov exponent does not obey any scaling. A scaling relation is valid not for minimal, but for some effective Lyapunov exponent, whose dependence on parameters is determined by scaling itself. If finite-size scaling is based on the effective Lyapunov exponent, existence of the 2D transition becomes not definite, but still rather probable. Interpretation of the results in terms of the Gell-Mann - Low equation is also given.

Soliton creation in quantum field theory: induced tunnelling in particle collisions

28 April 2005 in 11:30

D. Levkov, S. Sibiryakov (Nuclear Research Institute, Moscow State Univ)

We consider tunneling transitions between states separated by an energy barrier in a simple field theoretical model. We analyse the case of boundary soliton creation induced by collisions of a few highly energetic particles. We present semiclassical, but otherwise first principle, study of this process at all energies of colliding particles. We find that in the leading semiclassical approximation the probability of this process remains constant at high energies, and calculate the value of this constant.

Metallicheskaya" provodimost’, "perekhod" metall-dielektrik v 2D elektronnoi zhidkosti i soputstvuyushchie yavleniya

7 April 2005 in 11:30

V. Pudalov (FIAN)

Yazyk drobnykh proizvodnykh dlya zadach stokhasticheskogo transporta

24 March 2005 in 11:30

K.V. Chukbar (RNTs "Kurchatovskii institut")

Rassmatrivayutsya matematicheskie i fizicheskie aspekty deklariruemogo yazyka: sposoby vvedeniya drobnykh proizvodnykh, osnovnye osobennosti voznikayushchikh uravnenii ("zabyvanie" informatsii, "neizbavlyaemost’" ot drobnykh operatorov za schet ikh kratnogo primeneniya, svyaz’ s vykhodom za tsentral’nuyu predel’nuyu teoremu). Privodyatsya konkretnye primery fizicheskikh zadach, v kotorykh s neizbezhnost’yu voznikayut drobnye proizvodnye: modeli "poletov Levi" i "lovushek" (luchistyi perenos v koronal’noi plazme), snos turbulentnymi techeniyami, transport po fraktalam, effekty geometrii (malorazmernye sistemy). Obsuzhdaetsya svyaz’ prostranstvennoi i/ili vremennoi nelokal’nostei s sil’noi neravnovesnost’yu sistem, vliyanie na povedenie dopolnitel’nykh faktorov (konechnoi skorosti dvizheniya chastits, spetsificheskikh nachal’nykh uslovii).

Charge transfer between a superconductor and a hopping insulator

3 March 2005 in 11:30

V.I. Kozub, A.A. Zuzin, Y.M. Galperin, V. Vinokur

A theory of the low-temperature charge transfer between a superconductor and a hopping insulator is analyzed, and the corresponding interface resistance is calculated. This resistance is dominated by proposed electron-hole processes similar to Andreev reflection, but involving localized states in the insulator. The possibility of a new type of qubit where one of the quantum states is split between two spatially separated centers is discussed.

Anyons and haldane statistics: a dimensional reduction

24 February 2005 in 11:30

S. Ouvry (Orsay University)

An introduction to anyon statistics (particles in two dimensions beying nor Bose neither Fermi statistics) and to Haldane statistics (Hilbert space counting arguments) is made. The equation of state is given for a gas of anyons in the lowest Landau level of a strong magnetic field (Quantum Hall situation). By regularizing the system at long distance with an harmonic well, a link is established with the 1d Calogero-Moser model (Calogero in an harmonic well) and Haldane statistics. Recent tentatives to map the anyon model on a sphere to the Calogero-Sutherland model (Calogero on a circle) are finally discussed.

Mekhanizmy samoorganizatsii v nelineinykh otkrytykh sistemakh

3 February 2005 in 11:30

Andrei Polezhaev (FIAN)

Pervaya chast’ soobshcheniya nosit obzornyi kharakter. Budut privedeny primery sistem, demonstriruyushchikh prostranstvenno-vremennuyu samoorganizatsiyu, t.e. spontannyi perekhod v bolee uporyadochennoe sostoyanie. Budut sformulirovany obshchie printsipy postroeniya i issledovaniya sootvetstvuyushchikh modelei, perechisleny tipy opisyvaemykh imi struktur. Vo vtoroi chasti budet rasskazano o nekotorykh modelyakh konkretnykh sistem: elektro-khimicheskie struktury na poverkhnosti kletki, struktury, formiruemye koloniyami bakterii, struktury Lizeganga.

Dinamika otdel’nykh polimerov v potokakh s sil’noi sdvigovoi komponentoi

27 January 2005 in 11:30

K.S. Turitsyn

Rassmatrivaetsya vnutrennyaya dinamika otdel’nykh polimernykh molekul, nakhodyashchikhsya v sdvigovom potoke s nebol’shoi khaoticheskoi komponentoi. Takaya molekula budet ispytyvat’ sluchainoe aperiodicheskoe perevorachivanie iz-za sluchainykh sil. Izuchayutsya kak statisticheskie svoistva orientatsii polimera, tak i raspredelenie ego rastyazheniya. Provoditsya sravnenie teoreticheskikh predskazanii s eksperimental’nymi rezul’tatami.

Critical and low-temperature magnetic properties of itinerant cubic compounds with Dzialoshinskii-Moriya interaction (MnSi ets.)

13 January 2005 in 11:30

S. Maleyev (St. Peterburg)

Spin-shchelevye magnetiki s defektami

23 December 2004 in 11:30

A.I. Smirnov (IFP im. P.L. Kapitsy)

Budut rassmotreny dielektricheskie kristally s antiferromagnitnym vzaimodeistviem magnitnykh ionov i otsutstviem magnitnogo uporyadocheniya. Osnovnoe vnimanie planiruetsya udelit’ sleduyushchim voprosam: Eksperimenty, demonstriruyushchie netrivial’noe vliyanie defektov na spin-shchelevye sistemy, v chastnosti, navedenie magnitnogo poryadka nemagnitnymi primesyami v spin-paierlsovskom, khaldeinovskom i dimernom magnetikakh, perkolyatsionnyi kharakter takogo uporyadocheniya. Navedenie antiferromagnitnogo poryadka sil’nym magnitnym polem, "zakryvayushchim" shchel’ v spektre magnitnykh vozbuzhdenii. Issledovanie spinovykh vozbuzhdenii metodom magnitnogo rezonansa. Eksperimenty po issledovaniyu spektra i spinovoi struktury geometricheski frustrirovannykh magnetikov.

Kvantovanie gorizonta chernoi dyry, printsip sootvetstviya i golograficheskii predel

16 December 2004 in 11:30

I.B. Khriplovich (Institut yadernoi fiziki SO RAN, Novosibirsk)

Field theory for the global density of states distribution function in disordered conductors

9 December 2004 in 11:30

V.I. Yudson (Institut spektroskopii RAN, Troitsk)

A field-theoretical representation is suggested for distribution functions of global quantities (like conductance and electron global density of states) in extended disordered conductors. This opens a way to study the complete statistics of fluctuations. The approach is based on a functional integration over bi-local functions \Psi(r1, r2) instead of the integration over local functions in the usual functional representation for moments of physical quantities. The formalism allows one to perform the disorder averaging and to derive an analog of the usual nonlinear sigma-model - a "slow" functional of a supermatrix field Q(r; r1,r2) \sim \Psi(r, r1)\bar{\Psi}(r2, r). As an application of the formalism, the long-tail asymptotics of the global density of states distribution function P(\nu) is derived.

Formation of giant black holes in the center of galaxies

25 November 2004 in 11:30

A.V. Gurevich, K.P. Zybin

Nonlinear dynamics and formation of cold dark matter structures

18 November 2004 in 11:30

A.V. Gurevich, K.P. Zybin (FIAN)

Sound propagation in rouse polymer melts via generalized dynamic random phase approximation

11 November 2004 in 11:30

Igor Erukhimovich (Moscow State University)

An extended generalization of the dynamic random phase approximation (DRPA) for L-component polymer systems is presented. Unlike the original version of the DRPA, which relates the (L x L) matrices of the collective density-density time correlation functions and the corresponding susceptibilities of concentrated polymer systems to those of the tracer macromolecules and so-called broken-links system (BLS), our generalized DRPA solves this problem for the (5 x L)x(5 x L) matrices of the coupled susceptibilities and time correlation functions of the component number, kinetic energy and flux densities. The presented technique is used to study propagation of sound and dynamic form-factor in disentangled (Rouse) monodisperse homopolymer melt. The calculated ultrasonic velocity and absorption coefficient reveal substantial frequency dispersion. The relaxation time T is proportional to the degree of polymerization N, which is N times less than the time of relaxation of a single chain, which evidences strong dynamic screening due to interchain interaction. We discuss also some peculiarities of the Brillouin scattering in polymer and copolymer melts.

Field theory description of the polymer-induced many-body interaction and aggregation instability in colloid solutions

11 November 2004 in 11:30

Igor Erukhimovich (Moscow State University)

Starting from microscopic consideration we present a field theory descriptions of the polymer-colloid systems - the composite systems formed by both long polymer chains and relatively small (but large as compared to the monomers) particles. The peculiarity of such systems is that the ultraviolet divergencies in the corresponding field theory describe the polymer-colloid interactions and could be rigorously calculated. The infrared divergencies allow for the critical behavior of the system as the whole and in the present talk we take them into account within the mean-field approximation. The equation of state, phase diagram and the polymer-polymer and colloid-colloid correlation functions are calculated.

Kvantovo-kogerentnye dzhozefsonovskie sistemy

28 October 2004 in 11:30

Yu. Makhlin

My opishem nedavnie issledovaniya kvantovo-kogerentnykh sistem ("kubitov") v eksperimentakh s dzhozefsonovskimi kontaktami. V chastnosti, budet rassmotreno znachitel’noe uvelichenie vremeni poteri kogerentnosti i svyazannoe s etim poyavlenie vozmozhnostei dlya detal’nogo izucheniya prirody fluktuatsii i ikh vliyaniya na kogerentnost’. Takzhe budut rassmotreny sposoby provedeniya izmereniya kvantovogo sostoyaniya takikh sistem i kolichestvennye kharakteristiki protsessa izmereniya.

Negolonomnyi kontrol' i zaschita kogerentnosti slozhnykh kvantovykh sistem

7 October 2004 in 11:30

V. Akulin (Orsay University)

Single-shot readout of and energy relaxation in Josephson chage qubit

7 October 2004 in 11:30

Yu. Pashkin (NEC Research & Lebedev Institute)

Mikrovolnovaya spektroskopiya kompozitnykh fermionov i kollektivnye elektronnye vozbuzhdeniya v drobnom Kholle

30 September 2004 in 11:30

I.V. Kukushkin (IFTT)

Orientatsiya spinov elektricheskim tokom v geterostrukturakh: teoriya i eksperiment

16 September 2004 in 11:30

L.E. Golub (Fiziko-tekhnicheskii institut im. A.F. Ioffe, Peterburg)

Neravnovesnyi Fermi-gaz kak problema Rimana-Gil’berta

9 September 2004 in 11:30

B. Muzykantskii (University of Warwick, UK)

Monte-Carlo study of some orientational transitions in 2D

17 June 2004 in 11:30

Bertrand Berche (Universite Henri Poincare, Nancy, France)

In the numerical study of nematic-isotropic transition of liquid crystals, one usually considers lattice models with n-component spins interacting within nearest neighbours through Lengendre polynomials. In 2D,it is interesting to compare the phase transitions exhibited by such models with the special cases of XY and Heisenberg models. We present the results of Monte Carlo simulations analysed using Finite-Size scaling or conformal mapping. The results are not fully conclusive, but seem to confirm the possible occurrence of a first-order transition for a P4 interaction.

The quantum Hall effect: an experimental realization of the instanton vacuum

17 June 2004 in 11:30

A. Pruisken (University of Amsterdam, The Netherlands)

No annotation present.

Heisenberg constraints on mesoscopic and molecular amplifiers

10 June 2004 in 11:30

U. Gavish (LKB, Ecole Normale Superieure, Paris)

The Heisenberg principle puts constraints on the performances of linear amplifiers. We derive these constraints for the case of molecular or mesoscopic amplifiers with a narrow-band input. We then explain what physical processes create the noise which is necessarily added to the signal in order to satisfy these constraints. Finally we specify ways to minimize this noise.

Some aspects of practical quantum cryptography

3 June 2004 in 11:30

S.N. Molotkov (ISSP)

Nanoscale inhomogeneities and spectroscopies on BSCCO-2212

27 May 2004 in 11:30

Peter Hirschfeld (University of Florida)

In almost all high-temperature superconducting cuprate materials, doping naturally introduces disorder. Recent STM experiments have provided us with a remarkable window on the real space electronic structures which reflect this disorder, and found localized atomic scale resonances, nanoscale gap inhomogeneity, and long-range spatial modulations with well-defined wave vectors. I discuss to what extent these results can be understood in terms of BCS d-wave quasiparticle states interfering in the presence of many potential scatterers, and present both analytical results as well as numerical solutions of the Bogoliubov-de Gennes equations on 120x120 lattices. I further propose a ``realistic" model for the disorder, involving in-plane unitary scatterers and a smooth weak disorder component, which seems to work well for BSCCO-2212 but should be quite nonuniversal. Remaining discrepancies may point to novel physics such as correlation-induced magnetic moments, or coexistence with anomalous subdominant order. Implications for transport properties and angle-resolved photoemission using this model are also discussed.

Determining properties of dark energy in the Universe

20 May 2004 in 11:30

A.A. Starobinsky

Recent numerous observational data obtained from such independent sources as angular anisotropies of the cosmic microwave background radiation, large-scale gravitational clustering of galaxies and their clusters and observations of supernovae explosions at high redshifts prove convincingly that about 70% of the total energy density of matter in the present Universe is due to a new kind of matter in the Universe ("dark energy") which is non-baryonic, has negative pressure which modulus is very close to dark energy density (if the Einsteinian form of gravity field equations is assumed) and remains unclustered at all scales where the clustering of baryons and dust-like cold dark matter is seen. I discuss different forms of phenomenological description of dark energy properties, present limits on variation of dark energy density with redshift which follow from the most recent supernovae data and make a brief review of different theoretical models of dark energy including those in which it has a purely geometrical origin. The simplest possibility of dark energy being a cosmological constant and nothing more still remains a good fit to all existing observational data. However, more complicated behaviour including breaking of the weak energy condition for dark energy for redshifts z < 0.5 combined with some increase of its energy density with redshift for larger z is possible, too.

Critical currents and current-phase relation of SFS Josephson junctions

13 May 2004 in 11:30

V.V. Ryazanov (ISSP)

We have investigated experimentally the pi-state of Josephson SFS (superconductor-ferromagnet-superconductor) junctions. The origin of the pi-state is an oscillating and sign-reversal superconducting order parameter induced in the ferromagnet close to the SF-interface. Transition to the pi-state occurs for ferromagnetic interlayer thickness close to a half-period of the order parameter spatial oscillations. We have also observed back transition to conventional "0-state" at the F-layer thickness about of the period of the oscillations. Weak ferromagnetism of the F-layer (Cu/Ni alloy) allows us to fabricate thin-film Josephson SFS sandwiches with continuous homogeneous interlayers whose thickness (10-30 nm) is comparable with the pair-decay length in the ferromagnet and to observe a temperature 0-pi-transitions. We present also measurements of the current-phase relation (CPR) of SFS Josephson junctions as a function of temperature. The CPR is determined by incorporating the junction in a superconducting loop coupled to a dc SQUID, allowing measurement of the junction phase difference.

Quantum percolation in granular metals

22 April 2004 in 11:30

M.V. Feigel’man, A.S. Ioselevich, M.A. Skvortsov

Theory of quantum corrections to conductivity of granular metal films is developed for the realistic case of large randomly distributed tunnel conductances. Quantum fluctuations of intergrain voltages suppress mean conductance much stronger than its variance. At sufficiently low energies any distribution becomes broad, leading to strong local fluctuations of tunneling density of states. Percolative nature of metal-insulator transition is established by combination of analytic and numerical analysis of matrix renormalization group equations.

Andreev states near surfaces and in thin films of high-temperature superconductors

15 April 2004 in 11:30

Yu.S. Barash (ISSP)

Investigations of Andreev bound states in high-temperature superconductors will be shortly described in the Introduction. In the second and the third parts of the talk, new results of two papers will be represented. Effects of impurities, situated on (110) surface of d-wave superconductor, will be considered regarding the low-bias conductance of tunnel NIS junctions. Impurity-induced quasiparticle bound states on a pair-breaking surface of a d-wave superconductor are theoretically described, taking into account hybridization of impurity- and surface-induced Andreev states. Further, a theory for effects of surface disorder (of thin impurity surface layer) on the low-bias conductance of tunnel junctions is developed. In the third part of the talk we present analytical and numerical results for the electronic spectra of thin films (quantum wires) of a d-wave superconductor on a square lattice. The spectra of Andreev and other quasiparticle states, as well as the spatial and particle-hole structures of their wave functions, depend on interference effects caused by the presence of the surfaces and are qualitatively different for half-filled wires with even or odd number of chains. Effects of deviations from half-filling and results of the self-consistent calculations are also presented.

Puzzles of ultra-high -- energy cosmic rays (UHECRS)

1 April 2004 in 11:30

Dmitry Gorbunov (INR RAS)

Traveling in intergalactic medium protons of E>5*1019 eV start to lose energy rapidly due to pion production on cosmic microwave background (CMB) photons. Thus at higher energies only protons from local sources can reach the Earth. At lower energies protons cover a very large distance almost without attenuation. Based on this simple considerations the cut off in UHECRs spectrum has been predicted, that conflicts with experimental data. Although the statistic of anomalous events is low, one can try to provide an explanation for the observed behavior of the UHECR spectra. All attempts within the Standard Model of particle physics are failed. Therefore, possibly, UHECRs provide one of the few direct experimental evidences for the physics beyond the Standard Model. We are about to review the current status of the problems related to the absence of the cut off in UHECRs spectrum.

Coherent phenomena in multiply connected sns systems

25 March 2004 in 11:30

T.I. Baturina (Insitut fiziki poluprovodnikov, Novosibirsk)

Mesoscopic systems, consisting of a normal metal (N) or heavily doped semiconductor being in contact with a superconductor (S), have lately received much attention mainly because of a big variety of associated quantum effects. The key mechanism governing the carrier transport through the NS contact is the Andreev reflection. When a normal metal is placed between two superconducting electrodes another mechanism is involved in the charge transfer. It is the multiple Andreev reflection process (MAR). These phenomena result in nonlinear current-voltage characteristics, which exhibit an anomalous resistance dip at zero bias, the subharmonic energy gap structure, etc. Although at present the properties of single SNS junctions are well studied both theoretically and experimentally, the effect of the Andreev reflection and MAR process on the properties of a system consisting of a large number of normal metal regions connected by superconducting islands is practically not investigated. I will present the results of low-temperature transport measurements on two-dimensional arrays, on chains of SNS junctions and on single SNS junctions fabricated on the basis of superconducting PtSi film and perform a comparative analysis of their properties. Some unexpected coherence effects are found in multiply connected SNS systems, namely: (i) the gradual decrease of the effective suppression voltage for the excess conductivity observed at zero bias as the quantity of the SNS junctions increases, (ii) the strengthening of subharmonic energy gap structure in two-dimensional arrays of SNS junctions, (iii) a rich fine structure in the dV/dI-V dependences at dc bias voltages higher than the superconducting gap and corresponding to some multiples of 2Δ/e in chains of SNS junctions. All these results show that coherent phenomena governed by the Andreev reflection are not only maintained over the macroscopic scale but manifest novel pronounced effects as well.
I will discuss some possible approaches to explain the observed phenomena.

Relativistic doppler effect: universal spectra and zeptosecond pulses

18 March 2004 in 11:30

A. Pukhov, S. Gordienko

For the first time we report on a numerical observation of the train of zeptosecond pulses produced by reflection of a relativistically intense femtosecond laser pulse from the oscillating boundary of an overdense plasma because of the Doppler effect. These pulses promise to become a unique experimental and technological tool since their length is of order of the Bohr radius and the intensity is extremely high ~1019 W/cm2. We present the physical mechanism, analytical theory, and direct particle-in-cell simulations. We show that the harmonic spectrum is universal: the intensity of the n-th harmonic scales as 1/n3 for n < 4γ2, where γ is the largest γ-factor of the electron fluid boundary. The subattosecond pulses originate from this universal spectrum.

Border ledge fluctuations of crystal facets

4 March 2004 in 11:30

Michael Praehofer

Crystals in equilibrium consist of facets connected by rounded surfaces. On atomic scale the facet is surrounded by step lines or ledges whose density vanishes. There fluctuations are entropically reduced with respect to a single meandering ledge. We develop a scaling theory for the fluctuations and connect the statistics of the last ledge to the eigenvalue statistics of random matrices.

Semiclassical statistics of noise in mesoscopic systems

26 February 2004 in 11:30

K. Nagaev

A brief overview of the traditional Full Counting Statistics in mesoscopic systems will be given and principles of recently proposed semiclassical statistics of noise will be formulated. Special emphasis will be put on the frequency dependence of higher cumulants of noise.

Cluster model of local structure and bond orientational order in Lennard-Jones liquid

19 February 2004 in 11:30

V.N. Ryzhov (HPPI)

While the experimental and phenomenological knowledge of non-ergodic amorphous phases has been considerably improved in the last time, progress in the first-principle statistical mechanical studies of physical properties of supercooled liquids and glasses is much more slow. In this talk we discuss the microscopic approach to the study of the local structure and possible phase transitions in supercooled liquids based on the generalization of the density functional theory in classical statistical mechanics. A concept of the bond orientational order in simple liquids in two and three dimensions is reviewed, and the model of interacting cubic and icosahedral clusters in the Lennard-Jones liquid is proposed. In the framework of the model the analog of spin glass quenched disorder appears in a natural way in the Lennard-Jones system. The model is solved in the mean-field replica symmetric approximation. It is shown that the bond orientational order grows smoothly upon cooling, the symmetry of the ordered state being mainly cubic. The temperature of the possible glass transition is identified with the temperature at which the replica symmetry is broken.

Ordered states and phase transitions in two-dimensional frustrated XY-models

12 February 2004 in 11:30

S.E. Korshunov

1. Frustrated XY-models and their application.
2. Coulomb gas representation.
3. Ordered states and phase transitions at small frustration (f<<1).
4. The fully frustrated model (f=1/2)
with square or triangular lattice:
a) fractional vortices;
b) kink pairs unbinding on a domain wall and its consequences
for the sequence of phase transitions in the "bulk";
c) addition of further neighbors.
5. Ordered states in the vicinity of f=1/2.
6. Zero-energy domain walls. Removal of accidental degeneracy
by fluctuations (a few examples).

Mean-field replica approach for liquid-glass phase transition

5 February 2004 in 11:30

V. Dotsenko

In this talk we discuss recently developed statistical mechanical ideas for structural glasses. In particular we focus onto the first principle and mean-field computations for simple models of glasses with the two-body interparticle potentials. It is argued that on a qualitative level the equilibrium thermodynamics of the low-temperature glassy phase, as well as the liquid-glass phase transitions, can be described using the methods developed in the replica theory of spin-glasses and others disordered systems.

Bubble motion in inclined pipes

22 January 2004 in 11:30

A.Yu. Dem’yanov, N.A. Inogamov, A.M. Oparin

We analyze strongly nonlinear fluid motion with free surface in vertical, inclined, and horizontal pipes. The problem concerning rise of buoyant bubbles in vertical pipes is closely connected to the problem of Rayleigh-Taylor instability (instability of hydrostatic equilibrium when heavy fluid is imposed above light one). Inclined pipes are intensively investigated in connection with problems of transportation of gas-liquid or liquid-liquid flows. We develop a new approach to the problem of motion of large bubbles in wide pipes (large and wide mean that capillary scale is small). As against the previous approaches based on semiempirical methods, in the given work the analytical methods concerning the theory of potential are used. We do careful comparison of obtained solutions for two and three-dimensional spaces. It is shown that not always increase of dimension leads to an increase in velocity of rise of bubbles (as it is usually supposed). For the first time direct numerical simulations (DNS) are applied for studies of flows with free boundary in inclined pipes. We also use them in our work. They allow us, first, to check up accuracy of our analytical models and, second, to obtain the general picture of motion.

Weak crystallization in polymer systems

8 January 2004 in 11:30

Igor Erukhimovich (Condensed matter theory group, Institute of Physics, Johannes-Gutenberg-University of Mainz, Germany and A.N. Nesmeyanov Institute of Organoelement Compounds RAS, Moscow, Russia)

In this talk we review the current state of the theoretical and experimental results on polymer systems capable to undergo weak crystallization phase transition and present some of our new results in this field. The following issues will be addressed: 1. What are the block copolymers, polyelectrolytes, random and randomly correlated copolymers and why are they expected to undergo weak crystallization. 2. The basic idea of the Leibler microscopic theory of weak crystallization in block copolymers: relationship between the vertices of the phenomenological weak crystallization Hamiltonian and the structural correlators of the ideal macromolecules. 3. The phenomenological and microscopic theories of the conventional (body-centered cubic, hexagonal and lamellar) and non-conventional (gyroid, bcc2, face-centered cubic, simple cubic etc.) phases in block copolymers. 4. The SAXS data and other experimental methods to locate the phase diagrams of the weak crystallized polymer systems. Fluctuation (Brazovskii-Fredrickson-Helfand) effects and their experimental confirmation. 5. Non-centrosymmetric lamellar phase in block copolymer blends: experiment. 6. Phenomenological theory of non-centrosymmetric lamellar phase in the degenerate many-component weak crystallized systems.

Classical and quantum regimes of the superfluid turbulence

25 December 2003 in 11:30

G.E. Volovik

We discuss the turbulence of quantized vortex lines in connection with recent experiments in superfluid 3He [1]. This turbulence is governed by two dimensionless parameters. One of them is the intrinsic parameter q which characterizes the friction forces acting on a vortex moving with respect to the heat bath, with 1/q playing the same role as the Reynolds number Re = UR/ ν in classical hydrodynamics. It marks the transition between the "laminar" and "turbulent" regimes of vortex dynamics as suggested by recent experiments in Helsinki. The developed turbulence described by Kolmogorov cascade occurs when Re ›› 1 in classical hydrodynamics, and it must occur at q ‹‹ 1 in the superfluid hydrodynamics. Another parameter of the superfluid turbulence is the superfluid Reynolds number Res = UR/κ, which contains the circulation quantum κ characterizing quantized vorticity in superfluids. This parameter may regulate the crossover or transition between two classes of superfluid turbulence: (i) the classical regime of Kolmogorov cascade where vortices are locally polarized forming fat vortex tubes, so that the quantization is not important; (ii) the quantum turbulence whose properties are determined by the quantization of vorticity. The phase diagram of the dynamical vortex states is suggested [2]. [1] A.P. Finne, T. Araki, R. Blaauwgeers, V.B. Eltsov, N.B. Kopnin, M. Krusius, L. Skrbek, M. Tsubota, and G.E. Volovik, "An intrinsic velocity-independent criterion for superfluid turbulence", Nature 424, 1022-1025 (2003). [2] G.E. Volovik, "Classical and quantum regimes of the superfluid turbulence", Pis'ma ZhETF 78, 1021-1025 (2003).

Instanton-like baryon number violation in high-energy electroweak collisions

18 December 2003 in 11:30

F. Bezrukov, D. Levkov, V. Rubakov (INR, Moscow), C. Rebbi (U. Boston), P. Tinyakov (EPFL, Lausanne and INR, Moscow)

We make use of a semiclassical method for calculating the suppression exponent for topology changing transitions in high-energy collisions. In the Standard Model these processes are accompanied by violation of baryon and lepton number. By using a suitable computational technique we obtain results for s-wave scattering in a large region of initial data. Our results show that baryon and lepton number violation remains exponentially suppressed up to very high energies of at least 30 sphaleron masses (250 TeV). We also conclude that the known analytic approaches inferred from low energy expansion provide reasonably good approximations up to the sphaleron energy (8 TeV) only.

Duality in (2+1)D quantum elasticity: superconductivity and quantum nematic order

4 December 2003 in 11:30

J. Zaanen, Z. Nussinov, and S.I. Mukhin

Superfluidity and superconductivity are traditionally understood in terms of an adiabatic continuation from the Bose-gas limit. We do not use this approach. Taking the theory of quantum elasticity (describing phonons) in a 2+1 D Bose system as a literal quantum field theory, we show that superfluidity and superconductivity (in the EM charged case) emerge automatically when the shear rigidity of the elastic state is destroyed by the proliferation of topological defects (quantum dislocations). We consider the nematic states, corresponding with condensates of dislocations, with Burgers vectors as topological charges, under condition that disclinations remain massive. Due to glide principle for dislocations in 2+1 D the compression rigidity decouples from the dislocation condensate and stays massless. The shear rigidity does not decouple, and as a result the shear modes acquire a Higgs mass in the dual (dislocation) condensate. Hence, the fluids are characterized by an isolated massless compression mode and are therefore superfluids (Landau criterium reconfirmed!). We also consider different ordered/disordered states of Burgers vectors calling them "Coulomb nematic" and "quantum smectic" of a novel kind. Finally, we find that the Higgs mass of the shear gauge fields, becoming finite in the nematic quantum fluids, automatically causes a Higgs mass in the electromagnetic sector by a novel mechanism. Hence, a new hydrodynamical way of understanding the conventional electromagnetic Meissner state (superconducting state) is proposed.

Specific features of the insulator formed under the superconductor-insulator transition

20 November 2003 in 11:30

V.F. Gantmakher (Institute of Solid State Physics)

Various experimental observations of the magnetic-field-induced superconductor-insulator transition are described and compared with different theoretical models: one based on boson-vortex duality (Girvin, M.P.A. Fisher, et al.), next exploring the properties of granular superconductors (Beloborodov and Efetov) and the third analyzing effect of the superconducting fluctuations in the magnetic field at low temperature (Galitski and Larkin). All the models point to the existence of pairwise electron correlations at the Fermi-level of the insulator (so-called localized pairs) which should vanish in high magnetic fields. The localized pairs apparently come from the parity effect in ultra small quasigrains - local minima of the random potential which can admit only small limited number of electrons.

A short introduction to conformal field theory and its integrable perturbations, part II

13 November 2003 in 11:30

A.A. Belavin

No annnotation presented.

Superfluid and crystal phases in bilayer system

6 November 2003 in 11:30

E. YuriiLozovik (Institute of Spectroscopy, Troitsk)

Bilayer electron-hole and electron-electron systems are considered. Phase diagram, transport, drag effect, optical properties and Josephson phenomena will be reviewed. Liquid excitonic phase will be analyzed. Light backscattering in excitonic condensate will be reported. The electron-hole system in strong magnetic field will be considered.
Pairing in composite fermion bilayer is analyzed. The problem of BCS instability of compressible unpaired quantum Hall bilayer state at nu = 2 x 1/(2m) total filling fraction in large interlayer separation, d, limit is discussed. Microscopic analysis is carried out within the framework of composite fermion formalism. Gauge field fluctuations both diagonal and off-diagonal on layer indexes is taken into account. The first defines singular renormalization in one layer and leads to marginality of composite fermion liquid; the nondiagonal contribution defines interlayer interaction. Interlayer composite fermion attraction governed by antisymmetric density fluctuations is taken into account. The role of marginality on BCS pairing is analyzed. The quantum phase transition governed by interlayer separation is discussed.

Vortex phase diagram in clean and disordered layered superconductors

30 October 2003 in 11:30

Kees van der Beek (Ecole Polytechnique, France), S. Colson, M. Konczykowski, Y. Matsuda, M. Gaifullin, P. Gierlowski, I. Abalosheva, M. Li, P. Kes

The (B,T) phase diagram in layered superconductors in a magnetic field can be characterized by two transitions of the vortex lattice: a first order phase transition, commonly called vortex lattice melting, from a "vortex solid" to a "vortex liquid" without long range phase coherence, and a "depinning" transition above which no critical current can be measured. The two transitions follow quite different B(T) dependences, and can be studied independently by tuning material parameters, strength of disorder, or magnetic field. In the layered superconductor Bi2Sr2CaCu2O8, vortex fluctuations leading to either transition can be studied using the Josephson Plasma Resonance. In the first part of the talk, I shall present measurements in the "vortex solid" phase, at fields close to the first order transition field. The results show the predominant role of the vortex line tension, and the near-irrelevance of the vortex lattice shear modulus. This result is underscored by the observation of the first order transition in Bi2Sr2CaCu2O8 containing strong columnar pins. Finally, I shall present results obtained at higher fields, near the "depinning" or "delocalisation" transition. The results are put into perspective by a conjecture about the nature of the two transitions in magnetic field.

Magnetization reversal and two level fluctuations by spin-injection in a ferromagnetic metallic layer

30 October 2003 in 11:30

Jean-Eric Wegrowe (Ecole Polytechnique, France)

Slow magnetic relaxation and two level fluctuations measurements under high current injection is performed in single-contacted ferromagnetic nanostructures. The magnetic configurations of the samples are described by two metastable states of the uniform magnetization. The current-dependent effective energy barrier due to spin-transfer from the current to the magnetic layer is measured. The comparison between the results obtained with Ni nanowires of 6 μm length and 60 nm diameter, and Co (10 nm) / Cu (10 nm) / Co (30 nm) nanometric pillars of about 40 nm in diameter refined the characterization of this effect. It is shown that all observed features cannot be reduced to the action of a current dependent effective field. Instead, all measurements can be described in terms of an effective temperature, which depends on the current amplitude and direction, and on the magnetization state. The effective temperature is measured to be about 2000 K for 1 mA in nano-pillar structures, and 30 000 K for 1mA in Ni nanowires (far beyond the Curie temperature). The system is then analogous to an unstable open system. The effect of current induced magnetization reversal is interpreted as the balance of spin injection between both interfaces of the ferromagnetic layer.

A short intorduction to conformal fiel theory (CFT) and its integrable pertrubations

23 October 2003 in 11:30

A.A. Belavin

Part I. Critical behaviour and conformal symmetry.
Conformal symmetry in two dimensions.
Operator products expansion. Conformal bootstrap.
Classification of conformal field thories.
Minimal models of CFT. Spectrum of dimensions.
Correlation functions in CFT.

O bose-condensatsii mezh'yamnyh exitonov

9 October 2003 in 11:30

V.B. Timofeev

Self-consistent solutions in the weak turbulence and experiment

25 September 2003 in 11:30

V.E. Zakharov

CP-violation for B-mesons and status of neutrino oscillations

18 September 2003 in 11:30

M.I. Vysotsky (ITEP)

Modelling of exotic quantum systems on optical lattice

4 September 2003 in 11:30

Petr Fedichev (Universitet Innsbruck, Austria)

Growth in systems of vesicles and membranes

19 June 2003 in 11:30

E. Kats

A simple phenomenological model of nucleation and growth in systems of vesicles and membranes is presented and analyzed. It is shown that the process of vesicle growth can be understood as a certain "reaction" and the driving force for this reaction is determined by anharmonic contributions to the curvature elasticity. Assuming that the aggregation is controlled by diffusion a simple kinetic approach predicts that the average radius increases in time $t$ as $t^{1/6}$ in close agreement with experimental data.

Surface tension of liquid helium

19 June 2003 in 11:30

A. Dyugaev

The temperature dependence σ (T) of liquid He3 and He4 is determined in the intermediate temperature region when He3 and He4 are quantum but not degenerate liquids. This dependence is given by the universal law σ (T) - σ (0) ∝ T2 that is related to the contribution of the surface energy levels of helium vapor. These discrete levels also alter the mobility of electrons on the surface of liquid helium or of solid hydrogen. The work is joint with P. Grigoriev.

Collapses for non-linear Shröedinger equation

5 June 2003 in 11:30

Yu.N. Ovchinnikov

Collision group and renormalization of the Boltzmann collision integral

29 May 2003 in 11:30

V.L. Saveliev (Institute of Ionosphere)

On the basis of a recently discovered collision group, the Boltzmann collision integral is exactly rewritten in two parts. The first part describes the scattering of particles with small angles. In this part the infinity due to the infinite cross sections is extracted from the Boltzmann collision integral. Moreover, the Boltzmann collision integral is represented as a divergence of the flow in velocity space. Owing to this, the role of collisions in the kinetic equation can be interpreted in terms of the nonlocal friction force that depends on the distribution function.

Elastic turbulence: experiment and theory

15 April 2003 in 11:30

V. Lebedev

We are going to discuss a new phenomenon recently discovered experimentally by Groisman and Steinberg. It is the so-called elastic turbulence which is a random flow developed in weak polymer solutions at small Reynolds numbers. The reason for the chaotic state is in elastic instabilities which are relevant when the characteristic time of the flow fluctuations is of the order of the polymer relaxation time. The most interesting experimental data concern mixing, since the elastic turbulence is in some sense the ideal mixer. A research experimental information is obtained concerning statistical properties of the passive scalar advected by the chaotic flow in the elastic turbulence regime. The statistics admits a detailed theoretical derivation. We give a comparison of the theory and the experimental data.

On infinite symmetries in integrable lattice models and the corner transfer matrix approach

4 April 2003 in 11:30

Y. Pugai

During last ten years the algebraic approach based on vertex operators has been applied for finding exact integral representations for correlation functions and form-factors in many exactly solvable two-dimensional models of statistical mechanics. This approach can be treated as a natural generalization of the Baxter Corner Transfer Matrix method. Using off-critical RSOS models as an example I would like to briefly discuss some properties of corner transfer matrices and give their algebraic interpretation in the spirit of the conformal field theory Virasoro algebra approach. Finally I would like to report on some recent results for correlation functions of Z(N) symmetric models based on the deformed parafermionic algebra.

Boundary value problems for integrable PDE's

20 March 2003 in 11:30

A. Degaperis, S.V. Manakov, P. Santini (Dipartamento di Fisica, Universita di Roma la Sapienza)

We review recent developments in the study of the Dirichlet and Newmann boundary value problems for linear and soliton PDE's.

Kelvin-Helmholtz instability in superfluids and balck hole horizon at the brane separating two quantum vacua

13 March 2003 in 11:30

G.E. Volovik

An analog of black hole can be realized in the future experiments in Helsinki. The horizon can be constructed for the 'relativistic' ripplons (surface capillary-gravity waves) living on the 'brane' represented by the interface between two superfluid vacua, 3He-A and 3He-B, sliding along each other without friction. Similar experimental arrangement has been already used in ROTA experiments for the observation and investigation of the Kelvin-Helmholtz type of instability in superfluids.
The shear-flow instability in superfluids is characterized by two critical velocities. The lowest threshold which has been measured in recent experiments corresponds to appearance of the ergoregion for ripplons (the region where ripplons have negative energy in the frame of the environment). In the shallow-water geometry this will give rise to the black-hole event horizon in the effective metric experienced by ripplons. In the region beyond the ergosurface or horizon, the brane quantum vacuum is unstable due to interaction of brane matter (ripplons) with bulk matter (quasiparticles living in the higher-dimensional world of bulk superfluids). The development of this instability results in nucleation of vortices in 3He-B and shrinking of the black hole horizon. This mechanism of the black hole decay can be faster than due to the traditional Hawking radiation.
The second critical velocity, the proper Kelvin-Helmholtz instability threshold, corresponds to the 'physical' singularity inside the black hole, where the determinant of the effective metric becomes infinite.

Cosmology near singularity

6 March 2003 in 11:30

D. Podolsky

We discuss classical and quantum properties of several string-inspired cosmological models. The subject of main interest for us is their behaviour near the cosmological singularity where one should expect strong discrepancies between Einstein-Hilbert general relativity and gravitation described by string low-energy effective action.

Light-cone integral approach to the Landau-Pomeranchuk-Migdal effect in QED and QCD

20 February 2003 in 11:30

B.G. Zakharov

In 1953 Landau and Pomeranchuk predicted within classical electrodynamics that multiple scattering can suppress considerably bremsstrahlung of high energy charged particles in medium. Later, in 1956 Migdal developed a quantum theory of this effect (usually called the Landau-Pomeranchuk-Migdal effect).
In this talk I discuss a new approach to the LPM effect based on the path integral treatment of multiple scattering. The approach is also applicable to gluon emission from a fast quark in a hot QCD matter. The rate of photon (gluon) radiation by an electron (quark) in a medium is expressed in terms of the Green function of a two-dimensional Schrodinger equation with an maginary potential. In QED this potential is proportional to the dipole cross section for scattering of an e e- pair off an atom, while in QCD it is proportional to the cross section of interaction of the color singlet quark-antiquark-gluon system with a color center.
In the case of QED we compare theoretical predictions with the first accurate data on the LPM effect obtained at SLAC. For most of the targets our predictions are in excellent agreement with the experimental data.

Wetting transition in superconductivity

6 February 2003 in 11:30

V.I. Marchenko, E.R. Podolyak

Waves and particles in layered media

23 January 2003 in 11:30

V. Ignatovich

We deduce and demonstrate simple analytical formulas for calculation of scattering of waves and particles in multilayered systems. In particular, reflection and transmission in quantum mechanics for arbitrary periodic potentials with finite number of periods. Algorithm for preparation of supermirror, or filters. Calculation of bound levels splitting in periodic potentials. Diffraction in three dimensional periodic systems. New form of dynamical diffraction in single crystals.

Spin transport in superconducting hybrid structures

16 January 2003 in 11:30

N.M. Chtchelkatchev

Not long ago emerged new direction in mesoscopic physics dealing with spin transport in nanostructures (traditionally mesoscopic physics deals with (coherent) electron transport in nanostructures). One of the important questions is description of spin transport in superconducting hybrid mesoscopic structures. For example, consider a beam of spin-polarized electrons scattering from thin superconducting region. It turns out that the superconductor at certain conditions plays the role of spin-filter separating the spin-current from the charge current. Consider now a beam of Cooper pairs (supercurrent) going through a constriction from one superconductor to another one. The constriction plays the role of quantum dot for Bogoliubov quasiparticles (Andreev quantum dot (AQD) is a superconducting junction where Bogolyubov quasiparticles can be trapped in discrete Andreev levels). Andreev levels in superconducting junctions are in general spin-degenerate. However in the presence of magnetic/exchange field or spin-orbit interaction spin degeneracy is lifted. Sometimes it is feasible to manipulate individual spin-state in an AQD. It can be shown that AQD can be brought into spin-1/2 state. The coupling between spin and superconducting current facilitate manipulation and measurement of this state in comparison with common semiconductor quantum dots. AQD's coupled inductively can serve as a solid-state base for universal quantum computing.

Single-electron transport through the vortex core levels in clean superconductors

26 December 2002 in 11:30

N.B. Kopnin, A.S. Mel’nikov, V.M. Vinokur

We investigate the low temperature electron transport in N-S-N structures in the presence of vortex lines perpendicular to the interfaces. It is shown that, in the absence of elastic scattering at the interface, the single-electron transport along the vortices in clean superconductors is not determined by the density of states in vortex cores. Within the quasiclassical approach the vortex contribution to the transport is determined by resonance tunneling of electrons via vortex core levels. We calculate the thermal conductance in the direction along the magnetic field and show that it decays with an increase in the superconducting slab thickness.

Self-organization of the critical state in granular superconductor

19 December 2002 in 11:30

S.L. Ginzburg and N.E. Savitskaya (Petersburg Nuclear Physics Institute)

We study the critical state of a one-dimensional multijunction SQUID with a random arrangement of junctions in an increasing magnetic field. Using two mathematical models (system of differential equations for gauge-invariant phase differences and a simplified algorithm), we show that the system demonstrates a self- organized behavior. An intrinsic spatial randomness introduced into the model allows us to obtain self-organization in one-dimensional case under fully deterministic perturbation. We also show that our simplified algorithm represents a new model of a self-organized criticality.

Coulomb correlation effects in the tunelling spectroscopy of individual impurities

5 December 2002 in 11:30

P.I. Arseyev (Lebedev Physical Institute)

Some non-equilibrium Coulomb effects in resonant tunnelling through deep impurity states are analyzed. It is shown that corrections to the tunnelling vertex caused by the Coulomb interaction can result in nontrivial behavior of the tunnelling characteristics and should be taken into account. One encounters with effects similar to the Mahan edge singularities in the problem of X - ray absorption spectra in metals. One might expect in this situation a smeared power-law singularity in current-voltage characteristics near the threshold voltage.

Shedding and interaction of solitons in weakly disordered optical fibers

31 October 2002 in 11:30

M. Chertkov, Y. Chung, A. Dyachenko, I. Gabitov, I. Kolokolov, and V. Lebedev

Propagation of a soliton pattern through an optical fiber with weakly disordered dispersion is considered. Solitons, perturbed by this disorder, radiate, and, as a consequence, decay. The average radiation profile and the degradation law of a single soliton is found. The emergence of a long-range intra-channel interaction between the solitons, mediated by the radiation, is reported. We show that soliton in a multi-soliton pattern experience a random jitter: average force acting on a soliton is negligible and fluctuations of the soliton velocity are Gaussian, with a typical fluctuation proportional to square of the distance passed by the soliton in the fiber and to square root of the information rate (number of solitons per unit length of the fiber). We also present results of direct numerical simulation of the soliton decay and two-soliton interaction, confirming our theoretical analysis.

N=1 supersymmetric gauge theories and geometry

17 October 2002 in 11:30

K. Saraikin

We will review recent progress in gauge theories with minimal (N=1) supersymmetry: confinement, instanton corrections, superpotentials, relation with Seiberg-Witten theory etc. In particular, we will discuss how low-energy effective action of such theories can be reproduced in pure geometrical terms using certain (Calabi-Yau) three dimensional complex manifolds.

Trans-planckian particle creation in cosmology

26 September 2002 in 11:30

A.A. Starobinsky

If the Lorentz invariance is broken (or "deformed") at some large energy close to the Planckian one, so that the dispersion law for elementary particles ω(k) differs from the standard one, the expansion of the Universe may result in gravitational creation of pairs of particles and antiparticles with a very high energy. The expansion of the Universe (both at present time and in the early Universe) gradually redshifts momenta of all Fourier modes of a quantum field and transports them from the trans-Planckian region of very high momenta to the sub-Planckian region where the standard particle interpretation is valid. Then, if the WKB condition is violated somewhere in the trans-Planckian region, the field modes enter the sub-Planckian region in a non-vacuum state containing equal number of particles and antiparticles.
This effect, if exists at all, can be found or limited by cosmological observations. The most restrictive upper limit follows from the number of ultra-high energy cosmic rays created now. In turn, their total amount can be shown to be bounded by the cosmic diffuse gamma-ray background. This limit rules out the possibility to detect signatures of such short distance effects by studying the temperature anisotropy of the cosmic microwave background. On the other hand, a remarkable possibility that some part of observed ultra-high energy cosmic rays originates from new trans-Planckian physics remains open.

Statistical mechanics of magnetic-field sensitive structural glass

12 September 2002 in 11:30

Giancarlo Jug

Recent experiments on the thermal, dielectric and acoustic properties of multicomponent glasses at low temperatures have revealed an unusual response in some window-glasses to a weak applied magnetic field. A statistical-mechanics theory will be presented to explain quantitatively, at least in part, these puzzling experimental findings. The theory is based on an extension of the standard tunneling model for structural low-temperature glasses and on the mean-field theory of spin-glasses, suitably adapted to the problem.

Dynamics of Bose condensation

5 September 2002 in 11:30

V.E. Zakharov

Acceleration of chemical reactions by chaotic mixing

20 June 2002 in 11:30

V.V. Lebedev

A comprehensive theory of the binary chemical reaction A+B->C in chaotic flows at large Schmidt (Sc) and Damköhler (Da) numbers, and with initially injected equal (or close to equal) amounts of both chemicals, is developed. The combined effects of advection and diffusion are important and result in essential enhancement (in comparison with a situation without advection) of the overall reaction rate. Diffusion controls the fluxes of chemicals towards the interface separating the chemicals, while advection increases area of the interface. We identify four different stages of the spatio-temporal evolution. The chemicals are well separated during all but the final (and the only spatially uniform) stage. The relatively complex division of the evolution into the stages is due to finite-size effects which appear when the chemical reaction rate is controlled by the bulk, peripheral, and boundary domains of the flow.

Internal waves and synchronized precession in a cold vapor

13 June 2002 in 11:30

L. Levitov

It was shown by E. Bashkin in 1981 that exchange in a Boltzmann gas of bosons with several internal states leads to collective transport of internal polarization. The internal dynamics can be understood as Larmor precession in the presence of a torque induced by atoms on each other via exchange coupling. In a recent experiment carried out in JILA, collective waves of internal state polarization in a cold magnetically trapped Rb vapor were observed by a new spatially resolved technique. A generalized Bloch equation that includes interatomic exchange effects as well as orbital motion in the gas is derived and used to interpret the JILA experiment. It is predicted that exchange leads to formation of domains in which precession frequencies are synchronized.
(M. Oktel and L.L., PRL 88, 230403, 2002)

On the motion of muplicharge bubbles in helium.(short communication)

13 June 2002 in 11:30

R. Arhipov

No anntotation.

On integrable systems connected with quantum groups in root of unity

6 June 2002 in 11:30

A.A. Belavin

Centre of Quantum Group (QG) in root of unity is extended. It makes possible to perform Quantum Group reduction of Integrable model connected with the QG. It can be shown that after this Quantum Group reduction the transfer-matrices of the model satisfy the closed system of the truncated functional relations.

Quantization of some cubic Poisson brackets

6 June 2002 in 11:30

A. Odesskii

We discuss the problem of quantization of certain class of Poisson structures, for example {x,y}=z3, {y,z}=x3, {z,x}=y3. Our main tool is invariant pseudodifferential operators on the complex half-plane.

Simple interfacial model of surface-induced smectic layering in liquid crystals

30 May 2002 in 11:30

E.S. Pikina and V.E. Podnek

We propose simple interfacial model of surface-induced smectic layering (quantized wetting layer growth) observed just above the bulk isotropic-smectic A phase transition in liquid crystals [1]. The model generalizes known interfacial models of critical wetting and roughening transition. It is shown that smectic wetting in the layering regime is always incomplete. The comparison with experimental data is made.
[1] B.M.Ocko, A.Braslau, P.S.Pershan, J.Als-Nielsen, and M.Deutsch, Phys.Rev.Lett., 1986, vol. 57, p. 94

Possible realization of an ideal quantum computer in Josephson junction array with topologically protected degenerate ground states

23 May 2002 in 11:30

L.B. Ioffe and M.V. Feigelman

We introduce a new class of Josephson arrays which have non-trivial topology and exhibit a novel state at low temperatures. This state is characterized by long range order in a two Cooper pair condensate and by a discrete topological order parameter. These arrays have degenerate ground states with this degeneracy 'protected' from the external perturbations (and noise) by the topological order parameter. We show that in ideal conditions the low order effect of the external perturbations on this degeneracy is exactly zero and that deviations from ideality lead to only exponentially small effects of perturbations. We argue that this system provides a physical implementation of an ideal quantum computer with a built in error correction and show that even a small array exhibits interesting physical properties such as superconductivity with double charge, 4e, and extremely long decoherence times.

The ground state and excitations in 2deg in magnetic field at large Coulomb interaction

16 May 2002 in 11:30

S.V. Iordanski, A. Kashuba

Some general properties of possible classification of the ferromagnetic ground state are investigated. The spectrum of the low energy collective excitations consists of Kohn exciton and gapless spin exciton. It is shown that the energy of topological excitations (skyrmions) is lower than the cyclotron energy (at large Coulomb interaction) and does not contain the large exchange energy typical for opposite case of extremely large magnetic field.

Collapse in hydrodynamics and Kolmogorov spectrum

18 April 2002 in 11:30

E.A. Kuznetsov

Isotropisation of Bianchi I brane cosmological models

4 April 2002 in 11:30

A.V. Toporensky (Sternberg Astronomical Institute)

The problem of isotropisation of Bianchi I brane cosmological model is described. It is shown that unlike a standard scenario the presence of an ordinary matter with a positive pressure enlarges anisotropy of a brane at early stages of cosmological expansion (when brane corrections to Einstein equations are significant). A possible influence of an anisotropic stress on the brane dynamics is also discussed.

Hidden long range order in Heisenberg Kagome antiferromagnets

21 March 2002 in 11:30

A.V. Syromyatnikov (St. Petersburg)

We give a physical picture of the low-energy sector of the spin 1/2 Heisenberg Kagome antiferromagnet (KAF). It is shown that Kagome lattice can be presented as a set of stars which are arranged in a triangular lattice and contain 12 spins. Each of these stars has two degenerate singlet ground states which can be considered in terms of pseudospin. As a result of interaction between stars we get Hamiltonian of the Ising ferromagnet in magnetic field. So in contrast to the common view there is a long range order in KAF consisting of definite singlet states of the stars.

The threshold processes in external electromagnetic fields

21 March 2002 in 11:30

V.N. Rodionov, G.A. Kravtsova, and A.M. Mandel (Moscow)

The threshold processes in external electromagnetic fields of some configurations are considered. The decay of quasistationary states is studied by means of the probability equations. Starting with these equations, we obtain the expressions for complex energy as a function of the field. Moreover, asymptotics for Re and Im parts of the energy are studied. In particular, we prove the absence of the stable action of magnetic field for some configurations and discuss consequences of this result.

Bosonisation techniques in the theory of exactly solvable models

21 February 2002 in 11:30

M. Lashkevich

It is a review of bosonization techniques, their advantages and problems. These techniques take their origin in Baxter's corner transfer matrix approach and bosonization of conformal field theory. Bosonization makes it possible to calculate exactly short-range correlation functions and form factors in a class of lattice models. In the case of models of quantum field theory similar techniques are related to quantization in the Rindler coordinates and provide exact integral expressions for form factors.

Nuclear ferromagnetism induced Fulde-Ferrel-Larkin-Ovchinnikov state

24 January 2002 in 11:30

A.M. Dyugaev

We present a theoretical study of the influence of the nuclear ferromagnetism on superconductivity in the presence of the electron-nuclear spin interaction. It is demonstrated that in some metals, e.g. Rh, W, the BCS condensate imbedded in a matrix of ferromagnetically ordered nuclear spins should manifest the FFLO (Fulde-Ferrel-Larkin-Ovchinnikov) state. We outline that the optimal experimental conditions for observation of FFLO could be achieved by creation, via adiabatic nuclear demagnetization, of the negative nuclear spin temperatures. In this case the nuclear polarization points in the opposite to the external magnetic field direction and the electromagnetic part of the nuclear spin magnetization compensates the external magnetic field, while the exchange part creates the nonhomogeneous superconducting order parameter.

Charge-density wave (CDW) and spin-density-wave (SDW) phases induced by a magnetic field in low-dimensional solids

10 January 2002 in 11:30

A.G. Lebed

A cascade of the metal-CDW phase transitions (recently discovered by D.Anders et al.) and the cascades of the metal-SDW transitions (which are observed in some low-dimensional organic conductors) are theoretically analyzed. We calculate the transition temperatures and free energies of the CDW and SDW subphases induced by a magnetic field. For CDW, we predict novel kind of an angular resonance and a novel type of a metal-DW phase diagram. We discuss the connections of our results with the existing experimental data including the so-called "three-dimensional quantum Hall effect".

Critical fields in supreconductors

27 December 2001 in 11:30

Yu.N. Ovchinnikov

Effects of doping and disorder on the spin-Peierls state (experiment)

20 December 2001 in 11:30

S.V. Demishev (General Physics Institute of RAS)

1. Introduction. Organic and inorganic spin-Peierls materials. Universal properties of spin-Peierls materials: magnetic phase diagram and concentrational phase diagram. Specific case of CuGeO3.
2. Universality vs. experiment (cases of CuGeO3 and MEM(TCNQ)2). Discussion of the Mostovoi and Khomskii calculation of the concentrational phase diagram.
3. Outside the universal scenario: the case of CuGeO3 doped with magnetic impurities.
4. Specific problems of ESR in the 1D s=1/2 antifferomagnetic chains. Latest developments.

Josephson current between chiral superconductors

6 December 2001 in 11:30

Yu.S. Barash, A.M. Bobkov and M. Fogelstrom

We study chiral interface Andreev bound states and their influence on the Josephson current between clean superconductors. Possible examples are superconducting Sr2RuO_4 and the B-phase of the heavy-fermion superconductor UPt3. We show that, under certain conditions, the low-energy chiral surface states enhance the critical current of symmetric tunnel junctions at low temperatures. The enhancement is substantially more pronounced in quantum point contacts. In classical junctions dispersive chiral states result in a logarithmic dependence of the critical current. This logarithmic behavior contains the temperature, the barrier transparency and the broadening of the bound states, and depends on the detailed relation between these parameters. The Josephson current through the domain wall doesn't acquire this logarithmic enhancement, although the contribution from the bound states is important in this case as well.

Towards the theory of quantum black holes

22 November 2001 in 11:30

Victor Berezin (Institute for Nuclear Research RAS)

Everybody knows what the classical black holes are.
The main feature that characterizes black holes and distinguishes them from other physical objects is their universality. Such an universality is widely known as the "no hair conjecture". It means that everything that can be radiated away does radiate during the gravitational collapse, and the resulting black hole is described by only few parameters, namely, by its mass, angular momentum and gauge charges. The universal character of black holes allowed J.Bekenstein to put forward an analogy between black hole physics and thermodynamics. According to Bekenstein, the black hole is endowed by some temperature and entropy, the value of entropy being proportional to the area of the event horizon. The rigorous proof of four laws of thermodynamics for the most general stationary black holes was given by Bardeen, Carter and Hawking. And at the top of these is Hawking's discovery that a black hole does radiate as a black body with this very temperature. S. Hawking considered a quantized scalar field on the given Schwarzschild background and showed that it is nontrivial causal structure of the black hole metric that is responsible for the black body radiation. Such an effect is purely quantum, and the Hawking temperature is a generalization of the Unruh temperature seen by an uniformly accelerated observer in the flat spacetime. The analogy between these two effects illustrates the famous equivalence principle.
The discovery of the black hole evaporation opened, in a sense, the quantum era in the black hole physics. The matter is that the very definition of the black hole involves the notion of the so called event horizon (which is the boundary between geodesics that can escape to infinity and those that cannot). The event horizon can be determined only globally, and the procedure requires knowledge of the whole history. Since, due to evaporation, the black holes disappear (at least, if do not take into account the back reaction of the radiation on the spacetime metric) the very notion of the black hole becomes only approximate.
Why should we study quantum black holes? First, this problem is interesting by itself and it could provide additional links between General Relativity and Quantum Theory. Second, at the final stage of evaporation black holes are so small that quantum effects can no more be ignored. Third, small black holes can be formed by large enough fluctuations of both matter fields or spacetime metric in the Very Early Universe (the so called Primordial Black Holes) or in the course of vacuum phase transitions. But how small should be a black hole in order to be considered as a quantum object? On purely dimensional grounds using Newton's constant G, Planck's constant $hbar$ and velocity of light c, we are able to construct two different quantities with the dimension of length for some object of mass m, namely, the Compton length $lambdabar/mc$ and the gravitational (Schwarzschild) radius rg = 2 G m/c2. For masses much smaller than the Planckian mass mPl = $sqrt{hbar c/G}$ the gravitational radius is much smaller than the Compton length and the object is purely quantum (this also indicates that there may be no black holes with so small masses). If the mass is much higher than the Planckian mass, the Compton length is well inside the black hole horizon and in this case we are already have purely classical black holes (if it is possible, of course, to ignore the Hawking radiation). Thus, the range of quantum black hole masses is somewhere in-between. The first attempt to obtain the quantum black hole mass spectrum was due to J. Bekenstein. He noticed that an event horizon area for slowly evolving black holes is an adiabatic invariant. So, the usual quasiclassical quantization leads to an equidistant spectrum for a black hole surface area. In the case of the Schwarzschild black hole this results in the now famous square-root mass spectrum mBH∼$sqrt{n}$, where n is an integer quantum number. The same type of spectrum was then advocated by J.Bekenstein and S.Mukhanov later on by many others. It was shown also that such a spectrum is compatible with the Hawking radiation.
In what follows we confine ourselves with consideration of the Schwarzschild (neutral, nonrotating) black holes only. The very fact that the mass (total energy) of black holes depends on only one quantum number n can be viewed as a generalization of the "no hair" conjecture and confirms the universal character of black holes also on the quantum level. But we should pay some price for such a universality. And this price is that the every energy level is highly degenerate. Indeed, since the black hole entropy is proportional to the area of the horizon, and the latter has (approximately) an equidistant spectrum, the number of quantum states with the same total energy (mass) grows exponentially with the quantum number nThe real physical explanation of this phenomenon is still an open problem. In our opinion, this is because we do not yet know what is an object that could be called a quantum black hole. In other words, we need a definition. It seems it is the universality that could become the crucial feature which would distinguish quantum black holes from any other quantum object. It is worth noting that in the recent paper by G.Gour the equidistant spectrum for the black hole area and the exponential degeneracy of the energy levels have been taken as postulates. The author constructed the Hamiltonian operator and the algebra of observables for quantum Schwarzschild black holes and, thus, showed the selfconsistency of these two postulates. The abovementioned attempts to construct a theory of quantum black holes can be called phenomenological.
The equidistant (or any other) black hole area spectrum which leads to a discrete mass spectrum poses one serious problem. The classical, in our case - Schwarzschild, black hole state is described by only one parameter, its mass, irrespective of how this black hole has been formed. Let us suppose that the black hole is formed by the collapse of gravitating particles. The motion of these particles can be either bound or unbound, such qualitative difference in the history of the constituents in no way reflected in the mass of the resulting black hole. This is not surprising in classical theory. But in quantum theory it does makes a difference. The bound motions give rise to discrete mass spectra while the mass spectra for unbound motions are continuous. And if the black hole mass spectrum is just the mass (energy) spectrum of this system of particles (what is the case in classical theory) we can easily distinguish the black holes formed due to bound motion from that formed due to unbound motion. But this contradicts the principle of universality (quantum "no-hair" conjecture). Then, what is it that gives the discrete mass spectrum for quantum black holes? Clearly, we need a deeper insight into the nature of these objects.

Inhomogenious charged states and phase stratification for manganites

25 October 2001 in 11:30

M.Yu. Kagan, K.I. Kugel, D.I. Khomskii

Analiziruyutsya mekhanizmy elektronnogo fazovogo rassloeniya v oksidnykh materialakh tipa manganitov. Rassmotrenie provoditsya v ramkakh prostoy modeli kondo-reshetki s mezhuzel'nym kulonovskim ottalkivaniem elektronov. Eta model' pozvolyaet vyyavit' neustoychivost' odnorodnogo magnitnogo ili zaryadovogo uporyadocheniya otnositel'no obrazovaniya kapel'nykh struktur (magnitnykh polyaronov) v shirokoy oblasti parametrov fazovoy diagrammy. Issleduyutsya razlichnye tipy i formy magnitnykh polyaronov. Obsuzhdayutsya transportnye kharakteristiki i spektr shumov v fazovo-rassloennom sostoyanii.

Uniqueness of electrostatic solutions in the bulk of perfect crystals

18 October 2001 in 11:30

E.V. Kholopov (Institute of Inorganic Chemistry)

Although the investigation of lattice sums is a classical subject for more than a century, some problems concerned with their uniqueness in dependence on the mode of summation, as well as with the rate of convergence exist heretofore. In the present work a rigorous electrostatic theorem has been proved about the definite convergence of Coulomb sums over translation invariant lattices. As a result, any uniform potential contribution to bulk potentials is absent in perfect crystals. The topological nature of this issue is associated with the periodic boundary conditions invariant to the definition of the unit cell. The close relation between absolute local potentials and the bulk Coulomb energy is substantiated. It is principal that the analysis may be performed in terms of absolutely convergent series by means of the incorporation of fictitious charges appropriate to the case. As a result, the general criterion on admissible orders of the lattice summation is proposed. The shell-by-shell order of summation accounting for crystal fields is verified as universal. The numerical efficiency of the direct summation modified properly is exhibited in a set of various model cases, with including depolar sums. The topological nature of the Lorentz field becomes evident therefrom.

Topologically protected quantum bits from Josephson junction arrays

11 October 2001 in 11:30

L.B. Ioffe, M.V. Feigelman, A.S. Ioselevich, D.A. Ivanov, M. Troyer, G. Blatter

All physical implementations of quantum bits (qubits), carrying the information and computation in a putative quantum computer, have to meet the conflicting requirements of environmental decoupling while remaining manipulable through designed external signals. Protecting qubits from decoherence by exploiting topological stability, a qualitatively new proposal due to Kitaev, holds the promise for long decoherence times, but its practical physical implementation has remained unclear so far. Here, we show how strongly correlated systems developing an isolated two-fold degenerate quantum dimer-liquid groundstate can be used in the construction of topologically stable qubits. We propose two implementations based on Josephson junction arrays and show how to construct the gates shifting the amplitude and phase of individual qubits and enforcing the entanglement of two qubits.

This seminar was cancelled

4 October 2001 in 11:30

A.M. Gurin. Geometric attractor of an electron beam which has passed through a crystal. The Lemmlein algorithm assigns a cyclic interaction of a mathematical point with other (n+1) points of the n-dimensional Euclidean space. In this paper generalization A of the Lemmlein algorithm for an arbitrary number of points m situated in the n-dimensional Riemann space is proposed. Algorithm A generates a Markovian chain consisting of the finite number of combinatorially different strongly convergent attractors.

Weak turbulence. Present state of theory

27 September 2001 in 11:30

V.E. Zakharov

Brane-world effective action and origin of inflation

20 September 2001 in 11:30

A. Barvinsky (Lebedev Physical Institute)

We construct braneworld effective action in two brane Randall-Sundrum model and show that the radion mode plays the role of a scalar field localizing essentially nonlocal part of this action. Non-minimal curvature coupling of this field reflects the violation of AdS/CFT-correspondence for finite values of brane separation. Under small detuning of the brane tension from the Randall-Sundrum flat brane value, the radion mode can play the role of inflaton. Inflationary dynamics corresponds to branes moving apart in the field of repelling interbrane inflaton-radion potential and implies the existence acceleration stage caused by remnant cosmological constant at late (large brane separation) stages of evolution. We discuss the possibility of fixing initial conditions in this model within the concept of braneworld creation from the tunneling or no-boundary cosmological state, which formally replaces the conventional moduli stabilization mechanism.

The elasticity of single DNA molecules (a review)

28 November 2000 in 11:30

V. Golo (MSU)

The mechanical properties of the DNA molecule have been a subject of intense study for the last few years. The current approach is to consider DNA as a worm-like chain. The model allows for explaining major experimental results, but still there are questions to the effect, especially concerning the elastic behaviour as a function of the ionic strength of the solvent. In particular it contradicts the familiar model of elastic rod often used for describing DNA.

Instanton approach to quantum chemical dynamics

28 November 2000 in 11:30

V.A. Benderskii (ICP)

Quantum chemical dynamics is based on the eigenvalue problem for multidimensional vibration Hamiltonians with potential energy surfaces (PES) having at least two minima, which are associated with the initial and final quasi-stationary states, reactants and products of chemical reaction. Although a semiclassical approximation is to be valid, commonly used WKB methods appear to be ineffective for multidimensional problems due to singularities of WKB solutions on caustics. Instanton approach (IA) differs from WKB method by replacement of energy as the quantity of h-order from Gamilton-Jacobi equation into transport equation. IA allows us to solve the Landau-Zener problem in the configuration space representation and derive the quantization rules for intersecting diabatic potentials at an arbitrary value of adiabatic coupling. In multidimensional IA, the minimum action path (MAP) is found from the classical equation of motion and then the Euclidean action is calculated in the vicinity of MAP as the expansion over the powers of transverse displacements with tunneling coordinate dependent coefficients. Coherent-incoherent transitions in the asymmetric double-well potentials and vibration stimulated tunneling are discussed as examples of IA applications.

Gravitational fields described by integrable reductions of Einstein's field equations

14 November 2000 in 11:30

G.A. Alekseev (Steklov Institute)

Einstein's equations for gravitational fields in vacuum, the Einstein - Maxwell and Einstein - Maxwell - Weyl equations for gravitational, electromagnetic and massless Weyl spinor fields, some string theory induced gravity models with electromagnetic, axion and dilaton fields are known to become integrable, if the space-time admits the Abelian two-dimensional isometry group and all field components and their potentials are dependent on some two of the four space-time coordinates only. In the talk we consider a number of specific features of very rich and universal (i.e. common for all these integrable cases) internal structure of reduced Einstein's equations which gave rise to a development of some general and simple approach to solution of these equations which can be called as the "monodromy transform" approach. This approach has provided a convenient base for further development of some effective methods for construction of solutions with wanted physical and geometrical interpretation, superposition of some known field configurations, generation of infinite hierarchies of solutions with infinitely increasing number of parameters and gave rise to the linear algorithms for solutions of the Cauchy and characteristic initial value problems for the reduced Einstein's equations. We also discuss particular examples of the solutions corresponding to physically different types of field configurations, such as the black holes immersed into the external gravitational and electromagnetic fields, various types of waves with smooth profiles or distinct wavefronts colliding on the Minkowski background or propagating in some other space-times, the waves emitted by accelerated sources, dynamics of some inhomogeneous cosmological models, and describe their physical and geometrical properties.