12 research outputs found
Wave scattering by discrete breathers
We present a theoretical study of linear wave scattering in one-dimensional
nonlinear lattices by intrinsic spatially localized dynamic excitations or
discrete breathers. These states appear in various nonlinear systems and
present a time-periodic localized scattering potential for plane waves. We
consider the case of elastic one-channel scattering, when the frequencies of
incoming and transmitted waves coincide, but the breather provides with
additional spatially localized ac channels whose presence may lead to various
interference patterns. The dependence of the transmission coefficient on the
wave number q and the breather frequency Omega_b is studied for different types
of breathers: acoustic and optical breathers, and rotobreathers. We identify
several typical scattering setups where the internal time dependence of the
breather is of crucial importance for the observed transmission properties.Comment: 17 pages, 19 figures, submitted to CHAOS (Focus Issue
Rearrangement of the vortex lattice due to instabilities of vortex flow
With increasing applied current we show that the moving vortex lattice
changes its structure from a triangular one to a set of parallel vortex rows in
a pinning free superconductor. This effect originates from the change of the
shape of the vortex core due to non-equilibrium effects (similar to the
mechanism of vortex motion instability in the Larkin-Ovchinnikov theory). The
moving vortex creates a deficit of quasiparticles in front of its motion and an
excess of quasiparticles behind the core of the moving vortex. This results in
the appearance of a wake (region with suppressed order parameter) behind the
vortex which attracts other vortices resulting in an effective
direction-dependent interaction between vortices. When the vortex velocity
reaches the critical value quasi-phase slip lines (lines with fast vortex
motion) appear which may coexist with slowly moving vortices between such
lines. Our results are found within the framework of the time-dependent
Ginzburg-Landau equations and are strictly valid when the coherence length
is larger or comparable with the decay length of the
non-equilibrium quasiparticle distribution function. We qualitatively explain
experiments on the instability of vortex flow at low magnetic fields when the
distance between vortices . We speculate that a
similar instability of the vortex lattice should exist for even when
.Comment: 10 pages, 11 figure
Circuit theory of multiple Andreev reflections in diffusive SNS junctions: the incoherent case
The incoherent regime of Multiple Andreev Reflections (MAR) is studied in
long diffusive SNS junctions at applied voltages larger than the Thouless
energy. Incoherent MAR is treated as a transport problem in energy space by
means of a circuit theory for an equivalent electrical network. The current
through NS interfaces is explained in terms of diffusion flows of electrons and
holes through tunnel and Andreev resistors. These resistors in diffusive
junctions play roles analogous to the normal and Andreev reflection
coefficients in OTBK theory for ballistic junctions. The theory is applied to
the subharmonic gap structure (SGS); simple analytical results are obtained for
the distribution function and current spectral density for the limiting cases
of resistive and transparent NS interfaces. In the general case, the exact
solution is found in terms of chain-fractions, and the current is calculated
numerically. SGS shows qualitatively different behavior for even and odd
subharmonic numbers, and the maximum slopes of the differential resistance
correspond to the gap subharmonics. The influence of inelastic scattering on
the subgap anomalies of the differential resistance is analyzed.Comment: 14 pages, 9 figures, title and text revised, to appear in PR
AC Josephson effect in the long voltage-biased SINIS junction
Theory of non-stationary coherent effects is developed for
superconductor-normal-superconductor (SNS) structures with relatively strong
normal scattering on S/N interfaces (interface resistance is large compared to
intrinsic resistance of N metal). Analitical expressions are found for the
time-dependent anomalous Green functions induced in the N region under the
fixed-voltage-bias. The amplitude of the current oscillations is determined in
non-equilibrium conditions. Non-stationary correction to the distribution
function is calculated in high-temperature limit and found to be slowly
decreasing with the temperature, leading to the dominance of the
second-harmonic term in the Josepshon current at high temperatures and low
voltage.Comment: Final version accepted for publication in JETP Letters. Introduction
and discussion in the end of Sec.4 are extended, figure and few references
added, some numerical coefficients correcte
Nonequilibrium Josephson effect in mesoscopic ballistic multiterminal SNS junctions
We present a detailed study of nonequilibrium Josephson currents and
conductance in ballistic multiterminal SNS-devices. Nonequilibrium is created
by means of quasiparticle injection from a normal reservoir connected to the
normal part of the junction. By applying a voltage at the normal reservoir the
Josephson current can be suppressed or the direction of the current can be
reversed. For a junction longer than the thermal length, , the
nonequilibrium current increases linearly with applied voltage, saturating at a
value equal to the equilibrium current of a short junction. The conductance
exhibits a finite bias anomaly around . For symmetric
injection, the conductance oscillates -periodically with the phase
difference between the superconductors, with position of the minimum
( or ) dependent on applied voltage and temperature. For
asymmetric injection, both the nonequilibrium Josephson current and the
conductance becomes -periodic in phase difference. Inclusion of barriers
at the NS-interfaces gives rise to a resonant behavior of the total Josephson
current with respect to junction length with a period . Both
three and four terminal junctions are studied.Comment: 21 pages, 19 figures, submitted to Phys. Rev.
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