Russian Academy of Sciences

Landau Institute for Theoretical Physics

In Print

Poverkhnostnyi impedans na diffuznoi granitse kiral’nogo p-volnovogo sverkhprovodnika

16 November in 11:30

Ya.V. Fominov

Vychislena lokal’naya kompleksnaya provodimost’ i obuslovlennyi eyu poverkhnostnyi impedans na diffuznoi granitse kiral’nogo p-volnovogo sverkhprovodnika. Imenno kiral’noe p-volnovoe sostoyanie schitaetsya naibolee veroyatnym v sverkhprovodyashchem rutenate strontsiya Sr2RuO4. Ono anizotropnoe i pri etom polnost’yu shchelevoe (modul’ parametra poryadka fiksirovan, a faza zavisit ot napravleniya). My rassmatrivaem otklik na vneshnee elektromagnitnoe pole kak na podshchelevykh, tak i na nadshchelevykh chastotakh. Izucheny anomal’nye osobennosti poverkhnostnogo impedansa, svyazannye s generatsiei vblizi granitsy nechyotnykh po chastote sverkhprovodyashchikh korrelyatsii (sostoyanie tipa sverkhprovodimosti Berezinskogo). Teoreticheskie rezul’taty sopostavleny s izmereniyami poverkhnostnogo impedansa Sr2RuO4, provedyonnymi v IFTT. Nablyudaetsya kachestvennoe soglasie teorii i eksperimenta.
Doklad osnovan na rabote S. V. Bakurskiy, Ya. V. Fominov, A. F. Shevchun, Y. Asano, Y. Tanaka, M. Yu. Kupriyanov, A. A. Golubov, M. R. Trunin, H. Kashiwaya, S. Kashiwaya, and Y. Maeno, "Local impedance on a rough surface of a chiral p-wave superconductor", Phys. Rev. B 98, 134508 (2018); https://arxiv.org/pdf/1807.11735.pdf

Sverkhprovodyashchii spinovyi klapan v sistemakh so splavom Geislera

16 November in 11:30 (short)

Ya.V. Fominov

Provedeno teoreticheskoe soprovozhdenie eksperimentov po izmereniyu effekta sverkhprovodyashchego spinovogo klapana v sisteme tipa FFS (gde F — ferromagnetik, S — sverkhprovodnik). Effekt sostoit v tom, chto kriticheskaya temperatura Tc sistemy zavisit ot vzaimnoi orientatsii namagnichennostei dvukh ferromagnetikov. V eksperimente v kachestve srednego F sloya byl vzyat splav Geislera Co2Cr1-xFexAl, i eto pozvolilo usilit’ effekt (raznost’ Tc pri parallel’noi i antiparallel’noi orientatsii) po sravneniyu s ranee issledovannymi sistemami s zhelezom. Znak effekta zavisit ot tolshchiny sloya. Teoriya ob’yasnyaet poluchennye rezul’taty. Usilenie effekta okazyvaetsya svyazano s umen’shennoi velichinoi obmennogo polya v splave Geislera.
Doklad osnovan na sleduyushchikh rabotakh:
[1] A. Kamashev, A. Validov, N. Garif’yanov, Ya. Fominov, P. Leksin, J. Schumann, J. Thomas, V. Kataev, B. Büchner, I. Garifullin, "Isolation of proximity-induced triplet pairing channel in a superconductor/ferromagnet spin valve", EPJ Web of Conferences 185, 08001 (2018).
[2] A.A. Kamashev, A.A. Validov, J. Schumann, V. Kataev, B. Büchner, Ya.V. Fominov, I.A. Garifullin, "Increasing the performance of a superconducting spin valve using a Heusler alloy", Beilstein J. Nanotechnol. 9, 1764 (2018).

New integrals of motion for waves on the deep water with a free surface

16 November in 11:30 (short)

A.I. Dyachenko

Khorosho izvestno, chto v priblizhenii slaboi nelineinosti dlya voln na vode (teoriya slaboi turbulentnosti), kogda uchityvayutsya tol’ko chetyrekh-volnovye vzaimodeistviya, imeetsya integral dvizheniya - polnoe "chislo voln" (volnovoe deistvie). Volny na glubokoi vode mogut byt’ razdeleny na dve gruppy, begushchie vlevo i begushchie vpravo. Pokazano, chto osobye svoistva koeffitsienta chetyrekh-volnovogo vzaimodeistviya privodyat k sokhraneniyu ne tol’ko polnogo "chisla voln", no i dvukh novykh integralov dvizheniya: "chislo voln", begushchikh vlevo, i "chislo voln", begushchikh vpravo.

Non-Born effects in scattering of electrons in clean quasi-one-dimensional conductors

26 October in 11:30

A. S. Ioselevich, N. S. Peshcherenko

Quasi-one-dimensional systems demonstrate Van Hove singularities in the density of states $\nu_F$ and the resistivity $\rho$, occurring when the Fermi level $E$ crosses a bottom $E_N$ of some subband of transverse quantization. We demonstrate that the character of smearing of the singularities crucially depends on the concentration of impurities. There is a crossover concentration $n_c\propto |\lambda|$, $\lambda\ll 1$ being the dimensionless amplitude of scattering. For $n\gg n_c$ the singularities are simply rounded at $\varepsilon\equiv E-E_N\sim \tau^{-1}$ – the Born scattering rate. For $n\ll n_c$ the non-Born effects in scattering become essential, despite $\lambda\ll 1$. The peak of the resistivity is split: for $\varepsilon>0$ there is a broad maximum at $\varepsilon\propto \lambda^2$. For $\varepsilon\lt 0$ there is a deep minimum at $|\varepsilon|\propto n^2\ll \lambda^2$. The behaviour of $\rho$ below the minimum depends on the sign of $\lambda$. In case of repulsion $\rho$ monotonically grows with $|\varepsilon|$ and saturates for $|\varepsilon| \gg \lambda^2$. In case of attraction $\rho$ has sharp maximum at $|\varepsilon| \propto \lambda^2$. The latter feature is due to resonant scattering by quasistationary bound states that inevitably arise just below the bottom of each subband for any attracting impurity.

Electron-phonon cooling power in Anderson insulators

26 October in 11:30

M. V. Feigel'man, V. E. Kravtsov

A theory for electron-phonon energy exchange in Anderson insulators with long localization length is developed. The major contribution to the cooling power as a function of electron temperature is shown to be directly related to the correlation function of the local density of electron states, which is enhanced near the localization transition by multi-fractality and by the presence of Mott's resonant pairs of states. The theory we develop explains huge enhancement of the cooling power observed in insulating Indium Oxide films as compared to predictions of standard theory for disordered metals

The free field representation for the GL(1|1) WZW model revisited

12 October in 11:30

M. Lashkevich

The Wess—Zumino—Witten theory related to the GL(1|1) supergroup possesses some interesting features. On one hand, its structure is rather simple, but, on the other hand, it is an example of a so called logarithmic theory, i.e. a conformal field theory that contains fields whose correlation functions depend on distances logarithmically. The spectrum of conformal dimensions in this theory is continuous, and logarithmic operators appear at some degenerate points, including those of zero dimension. The free field representation is an effective tool to study models of the conformal field theory, and that of the GL(1|1) theory seems to be rather simple and well-studied in previous works. Nevertheless, on my opinion, not all advantages of this representation were used. In the present work, beside a more detailed calculation of the structure constants, the fusion and braiding matrices were studied. It was shown that in the vicinity of degenerate points it is possible to chose a basis of conformal blocks, which resolves degeneration. I show how this basis is related to the logarithmic operators of the theory.

Three-dimensional stability of leapfrogging quantum vortex rings

21 September in 11:30 (short)

V.P. Ruban

It is shown by numerical simulations within a regularized Biot-Savart law that dynamical systems of two or three leapfrogging coaxial quantum vortex rings having a core width $\xi$ and initially placed near a torus of radii $R_0$ and $r_0$, can be three-dimensionally (quasi-)stable in some regions of parameters $\Lambda=\ln(R_0/\xi)$ and $W=r_0/R_0$. At fixed $\Lambda$, stable bands on $W$ are intervals between non-overlapping main parametric resonances for different (integer) azimuthal wave numbers $m$. The stable intervals are most wide ($\Delta W\sim$ 0.01--0.05) between $m$-pairs $(1,2)$ and $(2,3)$ at $\Lambda\approx$ 4--12 thus corresponding to micro/mesoscopic sizes of vortex rings in the case of superfluid $^4$He. With four and more rings, at least for $W>0.1$, resonances overlap for all $\Lambda$ and no stable domains exist.

Synchronization of Conservative Parallel Discrete Event Simulations on a Small-World Network

7 September in 11:30

Lev N. Shchur и Liliia Ziganurova

We examine the question of the influence of sparse long-range communications on the synchronization in parallel discrete event simulations (PDES). We build a model of the evolution of local virtual times (LVT) in a conservative algorithm including several choices of local links. All network realizations belong to the small-world network class. We find that synchronization depends on the average shortest path of the network. The time profile dynamics are similar to the surface profile growth, which helps to analyze synchronization effects using a statistical physics approach. Without long-range links of the nodes, the model belongs to the universality class of the Kardar–Parisi–Zhang equation for surface growth. We find that the critical exponents depend logarithmically on the fraction of long-range links. We present the results of simulations and discuss our observations.