arXiv subjects

I. A. Shereshevskii

Publications and source records attributed to I. A. Shereshevskii.

12 recordsLinked to original sources

arXiv2021

Electron-phonon heat transfer in giant vortex states

We examine energy relaxation of non-equilibrium quasiparticles in different vortex configurations in ``dirty'' $s$-wave superconductors. The heat flow from the electronic subsystem to phonons in a mesoscopic superconducting disk with a radius of the order of several coherence lengths is calculated both in the Meissner and giant vortex states using the Usadel approach. The recombination process is shown to be strongly affected by interplay of the subgap states, located in the vortex core and in the region at the sample edge where the spectral gap $E_{\rm g}$ is reduced by the Meissner currents. In order to uncover physical origin of the results, we develop a semiquantitative analytical approximation based on the combination of homogeneous solutions of Usadel equations in Meissner and vortex states of a mesoscopic superconducting disc and analytically calculate the corresponding spatially resolved electron-phonon heat rates. Our approach provides an important information about non-equilibrium quasiparticles cooling by the magnetic-field induced traps in various mesoscopic superconducting devices.

cond-mat.supr-con↗

arXiv2019

Electronic structure of mesoscopic superconducting disk: Quasiparticle tunneling between the giant vortex core and disk edge

The electronic structure of the giant vortex states in a mesoscopic superconducting disk is studied in a dirty limit using the Usadel approach. The local density of states profiles are shown to be strongly affected by the effect of quasiparticle (QP) tunneling between the states localized in the vortex core and the ones bound to the sample edge. Decreasing temperature leads to a crossover between the edge-dominated and core-dominated regimes in the magnetic field dependence of the tunneling conductance. This crossover is discussed in the context of the efficiency of quasiparticle cooling by the magnetic field induced QP traps in various mesoscopic superconducting devices.

cond-mat.supr-con↗

arXiv2012

Hybridization and interference effects for localized superconducting states in strong magnetic field

Within the Ginzburg-Landau model we study the critical field and temperature enhancement for crossing superconducting channels formed either along the sample edges or domain walls in thin-film magnetically coupled superconducting - ferromagnetic bilayers. The corresponding Cooper pair wave function can be viewed as a hybridization of two order parameter (OP) modes propagating along the boundaries and/or domain walls. Different momenta of hybridized OP modes result in the formation of vortex chains outgoing from the crossing point of these channels. Near this crossing point the wave functions of the modes merge giving rise to the increase in the critical temperature for a localized superconducting state. The origin of this critical temperature enhancement caused by the wave function squeezing is illustrated for a limiting case of approaching parallel boundaries and/or domain walls. Using both the variational method and numerical simulations we have studied the critical temperature dependence and OP structure vs the applied magnetic field and the angle between the crossing channels.

cond-mat.supr-con↗

arXiv2010

Andreev transport in two-dimensional normal-superconducting systems in strong magnetic fields

The conductance in two-dimensional (2D) normal-superconducting (NS) systems is analyzed in the limit of strong magnetic fields when the transport is mediated by the electron-hole states bound to the sample edges and NS interface, i.e., in the Integer Quantum Hall Effect regime.The Andreev-type process of the conversion of the quasiparticle current into the superflow is shown to be strongly affected by the mixing of the edge states localized at the NS and insulating boundaries. The magnetoconductance in 2D NS structures is calculated for both quadratic and Dirac-like normal state spectra. Assuming a random scattering of the edge modes we analyze both the average value and fluctuations of conductance for an arbitrary number of conducting channels.

cond-mat.supr-con↗

arXiv2009

Vortex Core States in Superconducting Graphene

The distinctive features of the electronic structure of vortex states in superconducting graphene are studied within the Bogolubov-de Gennes theory applied to excitations near the Dirac point. We suggest a scenario describing the subgap spectrum transformation which occurs with a change in the doping level. For an arbitrary vorticity and doping level we investigate the problem of existence of zero energy modes. The crossover to a Caroli - de Gennes - Matricon type of spectrum is studied.

cond-mat.supr-con↗

arXiv2006

Enhanced vortex heat conductance in mesoscopic superconductors

Electronic heat transport along the flux lines in a long ballistic mesoscopic superconductor cylinder with a radius of the order of several coherence lengths is investigated theoretically using both semiclassical approach and the full quantum-mechanical analysis of the Bogoliubov--de Gennes equations. The semiclassical approach is constructed analogously to the Landauer transport theory in mesoscopic conductors employing the idea that heat is carried by the quasiparticle modes propagating along the vortex core. We show that the vortex heat conductance in a mesoscopic sample is strongly enhanced as compared to its value for a bulk superconductor; it grows as the cylinder radius decreases. This unusual behavior results from a strongly increased number of single-particle transport modes due to giant mesoscopic oscillations of energy levels, which originate from the interplay between the Andreev reflection at the vortex core boundary and the normal reflection at the sample edge. We derive the exact quantum-mechanical expression for the heat conductance and solve the Bogoliubov--de Gennes equations numerically. The results of numerical computations confirm the qualitative Landauer-type picture and allow us to take into account the partial reflections of excitations. We analyze the effect of surface imperfections on the spectrum of core excitations. We show that the giant oscillations of core levels and thus the essential features of the heat transport characteristic to ideal mesoscopic samples hold for a broad class of surface imperfections as well.

cond-mat.supr-con↗

arXiv2005

Giant oscillations of energy levels in mesoscopic superconductors

The interplay of geometrical and Andreev quantization in mesoscopic superconductors leads to giant mesoscopic oscillations of energy levels as functions of the Fermi momentum and/or sample size. Quantization rules are formulated for closed quasiparticle trajectories in the presence of normal scattering at the sample boundaries. Two generic examples of mesoscopic systems are studied: (i) one dimensional Andreev states in a quantum box, (ii) a single vortex in a mesoscopic cylinder.

cond-mat.supr-con↗

arXiv2004

Magnetization reversal of ferromagnetic nanodisc placed above a superconductor

Using numerical simulation we have studied a magnetization distribution and a process of magnetization reversal in nanoscale magnets placed above a superconductor plane. In order to consider an influence of superconductor on magnetization distribution in the nanomagnet we have used London approximation. We have found that for usual values of London penetration depth the ground state magnetization is mostly unchanged. But at the same time the fields of vortex nucleation and annihilation change significantly: the interval where vortex is stable enlarges on 100-200 Oe for the particle above the superconductor. Such fields are experimentally observable so there is a possibility of some practical applications of this effect.

cond-mat.supr-con↗

arXiv2002

Random groups in the optical waveguides theory

We propose a new approach to the mathematical description of light propagation in a single-mode fiber light-guide (SMFLG) with random inhomogeneities. We investigate statistics of complex amplitudes of the electric field of light wave by methods of the random group theory. We have analyzed the behavior of the coherence matrix of a monochromatic light wave and the polarization degree of a nonmonochromatic radiation in SMFLG with random inhomogeneities as the length of the fiber tends to infinity; in particular, we prove that limit polarization degree is equal to zero.

math-ph↗

arXiv2002

A finite dimensional analog of the Krein formula

I offer a simple and useful formula for the resolvent of a small rank perturbation of large matrices. I discuss applications of this formula, in particular, to analytical and numerical solving of difference boundary value problems. I present examples connected with such problems for the difference Laplacian and estimate numerical efficiency of the corresponding algorithms.

math-ph↗

arXiv2001

Dynamics and transformations of Josephson vortex lattice in layered superconductors

We consider dynamics of Josephson vortex lattice in layered superconductors with magnetic, charge (electrostatic) and charge-imbalance (quasiparticle) interactions between interlayer Josephson junctions taken into account. The macroscopic dynamical equations for interlayer Josephson phase differences, intralayer charge and electron-hole imbalance are obtained and used for numerical simulations. Different transformations of the vortex lattice structure are observed. It is shown that the additional dissipation due to the charge imbalance relaxation leads to the stability of triangular lattice.

cond-mat.supr-con↗

arXiv2000

Nonsingular vortices in (s+d)-wave superconductors

The structure of a single flux line in (s+d)-wave superconductors has been analyzed within the Ginzburg-Landau (GL) model generalized for two order parameter components. The fourfold symmetric singular vortex solution is shown to be unstable in a certain range of the GL parameters with respect to the mutual shift of s- and d- wave unit vortices. The resulting nonsingular vortex structure is studied both analytically and numerically.

cond-mat.supr-con↗