arXiv subjects

M. A. Skvortsov

Publications and source records attributed to M. A. Skvortsov.

43 records · Page 3Linked to original sources

arXiv2000

Quantum superconductor-metal transition in a proximity array

A theory of the zero-temperature superconductor-metal transition is developed for an array of superconductive islands (of size d) coupled via a disordered two-dimensional conductor with the dimensionless conductance g>>1. At T=0 macroscopically superconductive state of the array with the lattice spacing b>>d is destroyed at g < g_c \approx 0.1 ln^2(b/d). At high temperatures the normal-state resistance between neighboring islands at b=b_c is much smaller than h/4e^2.

cond-mat.supr-con↗

arXiv1999

Proximity Effect in Presence of Quantum Fluctuations

The effect of Coulomb interaction upon superconductive proximity effect in disordered metals is studied, employing newly developed Keldysh functional approach (cond-mat/9907358). We have calculated subgap Andreev conductance between superconductor and 2D dirty film, as well as Josephson coupling via such a film. Both two qualitatively different Coulomb effects - suppression of the tunneling density of states and disorder-enchanced repulsion in the Cooper channel - are shown to be important at sufficiently low temperatures.

cond-mat↗

arXiv1999

Keldysh action for disordered superconductors

Keldysh representation of the functional integral for the interacting electron system with disorder is used to derive microscopically an effective action for dirty superconductors. In the most general case this action is a functional of the 8 x 8 matrix Q(t,t') which depends on two time variables, and on the fluctuating order parameter field and electric potential. We show that this approach reproduces, without the use of the replica trick, the well-known result for the Coulomb-induced renormalization of the electron-electron coupling constant in the Cooper channel. Turning to the new results, we calculate the effects of the Coulomb interaction upon: i) the subgap Andreev conductance between superconductor and 2D dirty normal metal, and ii) the Josephson proximity coupling between superconductive islands via such a metal. These quantities are shown to be strongly suppressed by the Coulomb interaction at sufficiently low temperatures due to both zero-bias anomaly in the density of states and disorder-enhanced repulsion in the Cooper channel.

cond-mat.supr-con↗

arXiv1998

Level statistics inside the core of a superconductive vortex

Microscopic theory of the type of Efetov's supermatrix sigma-model is constructed for the low-lying electron states in a mixed superconductive-normal system with disorder. The developed technique is used for the study of the localized states in the core of a vortex in a moderately clean superconductor (1/Δ<< τ<< 1/ω_0 = E_F/Δ^2). At sufficiently low energies E << ω_{Th}, the energy level statistics is described by the "zero-dimensional" limit of this supermatrix theory, with the effective "Thouless energy" ω_{Th} \sim (ω_0/τ)^{1/2}. Within this energy range the result for the density of states is equivalent to that obtained within Altland-Zirnbauer random matrix model of class C. Nonzero modes of the sigma-model increase the mean interlevel distance ω_0 by the relative amount of the order of [2\ln(1/ω_0τ)]^{-1}.

cond-mat.mes-hall↗

arXiv1998

Weak antilocalization in a 2D electron gas with the chiral splitting of the spectrum

Motivated by the recent observation of the metal-insulator transition in Si-MOSFETs we consider the quantum interference correction to the conductivity in the presence of the Rashba spin splitting. For a small splitting, a crossover from the localizing to antilocalizing regime is obtained. The symplectic correction is revealed in the limit of a large separation between the chiral branches. The relevance of the chiral splitting for the 2D electron gas in Si-MOSFETs is discussed.

cond-mat.mes-hall↗

arXiv1997

Supersymmetric Model of a 2D Long-Range Bose Liquid

The model Hamiltonian of a two-dimensional Bose liquid (proposed earlier by Kane, Kivelson, Lee and Zhang as the Hamiltonian which has Jastrow-type wavefunctions as the ground-state solution), is shown to possess nonrelativistic supersymmetry. For the special value of the coupling constant $α=1/2$ the quantum mechanics described by this Hamiltonian is shown to be equivalent to the dynamics of (complex) eigenvalues of random Gaussian ensemble of normal complex matrices. For general $α$, an exact relation between the equal-time current-current and density-density correlation functions is obtained, and used to derive an asymptotically exact (at low wavevectors q) spectrum of single-particle excitations beyond the superfluid ground-state (realized at low $α$'s). The ground-state at very large $α$ is shown to be of ``Quantum Hexatic" type, possessing long-range orientational order and quasi-long-range translational order but with zero shear modulus. Possible scenaria of the ground-state phase transitions as function of $α$ are discussed.

cond-mat.mes-hall↗

arXiv1996

Anomalous flux-flow dynamics in layered type-II superconductors at low temperatures

Low-temperature dissipation due to vortex motion in strongly anisotropic type-II superconductors with a moderate disorder ($Δ^2/E_F \ll \hbar/τ\ll Δ$) is shown to be determined by the Zener-type transitions between the localized electronic states in the vortex core. Statistics of these levels is described by the random matrix ensemble of the class C defined recently by Atland and Zirnbauer [cond-mat/9602137], so the vortex motion leads naturally to the new example of a parametric statistics of energy levels. The flux-flow conductivity $σ_{xx}$ is a bit lower than the quasiclassical one and {\it grows} slowly with the increase of the electric field.

cond-mat↗