187 research outputs found
Excitation spectrum of a 2D long-range Bose-liquid with a supersymmetry
We have studied excitation spectrum of the specfic 2D model of strongly
interacting Bose particles via mapping of the many-body Schrodinger equation in
imaginary time to the classical stochastic dynamics. In a broad range of
coupling strength a roton-like spectrum is found, with the roton gap
being extremely small in natural units. A single quantum phase transition
between strongly correlated supefluid and quantum Berezinsky crystal is found.Comment: 6 pages, 6 figure
Mean field theory for driven domain walls in disordered environments
We study the mean field equation of motion for driven domain walls in random
media. We discuss the two cases of an external constant as well as an
oscillating driving force. Our main focus lies on the critical dynamics close
to the depinning transition, which we study by analytical and numerical
methods. We find power-law scaling for the velocity as well as the hysteresis
loop area.Comment: 16 pages, 19 figures, submitted to Phys. Rev.
Proximity-induced superconductivity in graphene
We propose a way of making graphene superconductive by putting on it small
superconductive islands which cover a tiny fraction of graphene area. We show
that the critical temperature, T_c, can reach several Kelvins at the
experimentally accessible range of parameters. At low temperatures, T<<T_c, and
zero magnetic field, the density of states is characterized by a small gap
E_g<T_c resulting from the collective proximity effect. Transverse magnetic
field H_g(T) E_g is expected to destroy the spectral gap driving graphene layer
to a kind of a superconductive glass state. Melting of the glass state into a
metal occurs at a higher field H_{g2}(T).Comment: 4 pages, 3 figure
Coherent transport in Josephson-Junction rhombi chain with quenched disorder
We consider a chain of Josephson-junction rhombi (proposed originally by
Doucot and Vidal) in quantum regime. In a regular chain with no disorder in the
maximally frustrated case when magnetic flux through each rhombi \Phi_r is
equal to one half of superconductive flux quantum \Phi_0, Josephson current is
due to correlated transport of pairs of Cooper pairs, i.e. charge is quantized
in units of . Sufficiently strong deviation \delta\Phi =|\Phi_r-\Phi_0/2| >
\delta\Phi^c from the maximally frustrated point brings the system back to
usual -quantized supercurrent. For a regular chain \delta\Phi^c was
calculated by us previously. Here we present detailed analysis of the effect of
quenched disorder (random stray charges and random fluxes piercing rhombi) on
the pairing effect.Comment: 21 pages, 5 figure
Universal and non-universal tails of distribution functions in the directed polymer and KPZ problems
The optimal fluctuation approach is applied to study the most distant
(non-universal) tails of the free-energy distribution function P(F) for an
elastic string (of a large but finite length L) interacting with a quenched
random potential. A further modification of this approach is proposed which
takes into account the renormalization effects and allows one to study the most
close (universal) parts of the tails. The problem is analyzed for different
dimensions of a space in which the polymer is imbedded. In terms the stochastic
growth problem, the same distribution function describes the distribution of
heights in the regime of a non-stationary growth in a situation when an
interface starts to grow from a flat configuration.Comment: 17 pages, 2 figures, the final version, two paragraphs added to the
conclusio
Coulomb Blockade of Proximity Effect at Large Conductance
We consider the proximity effect in a normal dot coupled to a bulk
superconducting reservoir by the tunnel contact with large normal conductance.
Coulomb interaction in the dot suppresses the proximity minigap induced in the
normal part of the system. We find exact expressions for the thermodynamic and
tunneling minigaps as functions of the junction's capacitance. The tunneling
minigap interpolates between its proximity-induced value in the regime of weak
Coulomb interaction to the Coulomb gap in the regime of strong interaction. In
the intermediate case a non-universal two-step structure of the tunneling
density of states is predicted. The charge quantization in the dot is also
studied.Comment: 4 pages (RevTeX), 3 figures. Version 2: minor corrections, a figure
and two references adde
Eigenfunction fractality and pseudogap state near superconductor-insulator transition
We develop a theory of a pseudogap state appearing near the
superconductor-insulator transition in strongly disordered metals with
attractive interaction. We show that such an interaction combined with the
fractal nature of the single particle wave functions near the mobility edge
leads to an anomalously large single particle gap in the superconducting state
near SI transition that persists and even increases in the insulating state
long after the superconductivity is destroyed. We give analytic expressions for
the value of the pseudogap in terms of the inverse participation ratio of the
corresponding localization problem
Josephson Effect in a Coulomb-blockaded SINIS Junction
The problem of Josephson current through Coulomb-blocked nanoscale
superconductor-normal-superconductor structure with tunnel contacts is
reconsidered. Two different contributions to the phase-biased supercurrent are
identified, which are dominant in the limits of weak and strong Coulomb
interaction. Full expression for the free energy valid at arbitrary Coulomb
strength is found. The current derived from this free energy interpolates
between known results for weak and strong Coulomb interaction as phase bias
changes from 0 to pi. In the broad range of Coulomb strength the current-phase
relation is substantially non-sinusoidal and qualitatively different from the
case of semi-ballistic SNS junctions. Coulomb interaction leads to appearance
of a local minimum in the current at some intermediate value of phase
difference applied to the junction.Comment: 5 pages, 2 EPS figures, JETP Letters style file include
Theory of 4e versus 2e supercurrent in frustrated Josepshon-junction rhombi chain
We consider a chain of Josepshon-junction rhombi (proposed originally in
\cite{Doucot}) in quantum regime, and in the realistic case when charging
effects are determined by junction capacitances. In the maximally frustrated
case when magnetic flux through each rhombi is equal to one half of
superconductive flux quantum , Josepshon current is due to correlated
transport of {\em pairs of Cooper pairs}, i.e. charge is quantized in units of
. Sufficiently strong deviation from the maximally frustrated point brings the system back to
usual -quantized supercurrent. We present detailed analysis of Josepshon
current in the fluctuation-dominated regime (sufficiently long chains) as
function of the chain length, ratio and flux deviation .
We provide estimates for the set of parameters optimized for the observation of
-supercurrent.Comment: 23 pages, 9 figure
Order and Creep in Flux Lattices and CDWs Pinned by Planar Defects
The influence of randomly distributed point impurities \emph{and} planar
defects on the order and transport in type-II superconductors and related
systems is considered theoretically. For planar defects of identical
orientation the flux line lattice exhibits a new glassy phase dominated by the
planar defects with a finite compressibility, a transverse Meissner effect,
large sample to sample fuctuations of the susceptibility and an exponential
decay of translational long range order. The flux creep resistivity for
currents parallel to the defects is .
Strong disorder enforces an array of dislocations to relax shear strain
- ā¦