940 research outputs found
Self-dual Ginzburg-Landau vortices in a disk
We study the properties of the Ginzburg-Laundau model in the self-dual point
for a two-dimensional finite system . By a numerical calculation we analyze the
solutions of the Euler-Lagrange equations for a cylindrically symmetric ansatz.
We also study the self-dual equations for this case. We find that the minimal
energy configurations are not given by the Bogomol'nyi equations but by
solutions to the Euler Lagrange ones. With a simple approximation scheme we
reproduce the result of the numerical calculation.Comment: 8 pages, 4 figures, RevTex macro
Weak Localization and Antilocalization in Topological Insulator Thin Films with Coherent Bulk-Surface Coupling
We evaluate quantum corrections to conductivity in an electrically gated thin
film of a three-dimensional (3D) topological insulator (TI). We derive
approximate analytical expressions for the low-field magnetoresistance as a
function of bulk doping and bulk-surface tunneling rate. Our results reveal
parameter regimes for both weak localization and weak antilocalization, and
include diffusive Weyl semimetals as a special case.Comment: After publication, we have noticed and corrected two small but
potentially misleading typographic errors in Eqs. (2.27) and (2.29), where
the definitions of \tau_s and \tau_v were mistakenly switched. Once these
typographic errors are fixed, all the results remain unchanged. An Erratum
will be published in PR
Vortex nucleation through edge states in finite Bose-Einstein condensates
We study the vortex nucleation in a finite Bose-Einstein condensate. Using a
set of non-local and chiral boundary conditions to solve the
Schrdinger equation of non-interacting bosons in a rotating trap, we
obtain a quantitative expression for the characteristic angular velocity for
vortex nucleation in a condensate which is found to be 35% of the transverse
harmonic trapping frequency.Comment: 24 pages, 8 figures. Both figures and the text have been revise
Mesoscopic fluctuations in the spin-electric susceptibility due to Rashba spin-orbit interaction
We investigate mesoscopic fluctuations in the spin polarization generated by
a static electric field and by Rashba spin-orbit interaction in a disordered 2D
electron gas. In a diagrammatic approach we find that the out-of-plane
polarization -- while being zero for self-averaging systems -- exhibits large
sample-to-sample fluctuations which are shown to be well within experimental
reach. We evaluate the disorder-averaged variance of the susceptibility and
find its dependence on magnetic field, spin-orbit interaction, dephasing, and
chemical potential difference.Comment: 4 pages, 4 figure
Coherent Umklapp Scattering of Light from Disordered Photonic Crystals
A theoretical study of the coherent light scattering from disordered photonic
crystal is presented. In addition to the conventional enhancement of the
reflected light intensity into the backscattering direction, the so called
coherent backscattering (CBS), the periodic modulation of the dielectric
function in photonic crystals gives rise to a qualitatively new effect:
enhancement of the reflected light intensity in directions different from the
backscattering direction. These additional coherent scattering processes,
dubbed here {\em umklapp scattering} (CUS), result in peaks, which are most
pronounced when the incident light beam enters the sample at an angle close to
the the Bragg angle. Assuming that the dielectric function modulation is weak,
we study the shape of the CUS peaks for different relative lengths of the
modulation-induced Bragg attenuation compared to disorder-induced mean free
path. We show that when the Bragg length increases, then the CBS peak assumes
its conventional shape, whereas the CUS peak rapidly diminishes in amplitude.
We also study the suppression of the CUS peak upon the departure of the
incident beam from Bragg resonance: we found that the diminishing of the CUS
intensity is accompanied by substantial broadening. In addition, the peak
becomes asymmetric.Comment: LaTeX, 8 two-column pages, 6 figures include
Anderson localization of a Bose-Einstein condensate in a 3D random potential
We study the effect of Anderson localization on the expansion of a
Bose-Einstein condensate, released from a harmonic trap, in a 3D random
potential. We use scaling arguments and the self-consistent theory of
localization to show that the long-time behavior of the condensate density is
controlled by a single parameter equal to the ratio of the mobility edge and
the chemical potential of the condensate. We find that the two critical
exponents of the localization transition determine the evolution of the
condensate density in time and space.Comment: 4 pages, 2 figure
Transverse confinement of waves in 3D random media
We study the transmission of a tightly focused beam through a thick slab of
3D disordered medium in the Anderson localized regime. We show that the
transverse profile of the transmitted beam exhibits clear signatures of
Anderson localization and that its mean square width provides a direct measure
of the localization length. For a short incident pulse, the width is
independent of absorption.Comment: 4 pages, 3 figure
Quantum oscillations in mesoscopic rings and anomalous diffusion
We consider the weak localization correction to the conductance of a ring
connected to a network. We analyze the harmonics content of the
Al'tshuler-Aronov-Spivak (AAS) oscillations and we show that the presence of
wires connected to the ring is responsible for a behaviour different from the
one predicted by AAS. The physical origin of this behaviour is the anomalous
diffusion of Brownian trajectories around the ring, due to the diffusion in the
wires. We show that this problem is related to the anomalous diffusion along
the skeleton of a comb. We study in detail the winding properties of Brownian
curves around a ring connected to an arbitrary network. Our analysis is based
on the spectral determinant and on the introduction of an effective perimeter
probing the different time scales. A general expression of this length is
derived for arbitrary networks. More specifically we consider the case of a
ring connected to wires, to a square network, and to a Bethe lattice.Comment: 17 pages, 7 eps figure
Nonuniversal dynamic conductance fluctuations in disordered systems
Sample-to-sample fluctuations of the time-dependent conductance of a system
with static disorder have been studied by means of diagrammatic theory and
microwave pulsed transmission measurements. The fluctuations of time-dependent
conductance are not universal, i.e., depend on sample parameters, in contrast
to the universal conductance fluctuations in the steady-state regime. The
variance of normalized conductance, determined by the infinite-range intensity
correlation C_3(t), is found to increase as a third power of delay time from an
exciting pulse, t. C_3(t) grows larger than the long-range intensity
correlation C_2(t) after a time t_q ~ ^{1/2} t_D (t_D being the diffusion
time, being the average dimensionless conductance).Comment: Revised version, 6 pages, 5 figure
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