2,256 research outputs found
Magnetoconductivity of low-dimensional disordered conductors at the onset of the superconducting transition
Magnetoconductivity of the disordered two- and three-dimensional
superconductors is addressed at the onset of superconducting transition. In
this regime transport is dominated by the fluctuation effects and we account
for the interaction corrections coming from the Cooper channel. In contrast to
many previous studies we consider strong magnetic fields and various
temperature regimes, which allow to resolve the existing discrepancies with the
experiments. Specifically, we find saturation of the fluctuations induced
magneto-conductivity for both two- and three-dimensional superconductors at
already moderate magnetic fields and discuss possible dimensional crossover at
the immediate vicinity of the critical temperature. The surprising observation
is that closer to the transition temperature weaker magnetic field provides the
saturation. It is remarkable also that interaction correction to
magnetoconductivity coming from the Cooper channel, and specifically the so
called Maki-Thompson contribution, remains to be important even away from the
critical region.Comment: 4 pages, 1 figur
Entanglement entropy in one-dimensional disordered interacting system: The role of localization
The properties of the entanglement entropy (EE) in one-dimensional disordered
interacting systems are studied. Anderson localization leaves a clear signature
on the average EE, as it saturates on length scale exceeding the localization
length. This is verified by numerically calculating the EE for an ensemble of
disordered realizations using density matrix renormalization group (DMRG). A
heuristic expression describing the dependence of the EE on the localization
length, which takes into account finite size effects, is proposed. This is used
to extract the localization length as function of the interaction strength. The
localization length dependence on the interaction fits nicely with the
expectations.Comment: 5 pages, 4 figures, accepted for publication in Physical Review
Letter
Influence of trigonal warping on interference effects in bilayer graphene
Bilayer graphene (two coupled graphitic monolayers arranged according to Bernal stacking) is a two-dimensional gapless semiconductor with a peculiar electronic spectrum different from the Dirac spectrum in the monolayer material. In particular, the electronic Fermi line in each of its valleys has a strong p -> -p asymmetry due to trigonal warping, which suppresses the weak localization effect. We show that weak localization in bilayer graphene may be present only in devices with pronounced intervalley scattering, and we evaluate the corresponding magnetoresistance
Nonequilibrium mesoscopic conductance fluctuations
We investigate the amplitude of mesoscopic fluctuations of the differential
conductance of a metallic wire at arbitrary bias voltage V. For non-interacting
electrons, the variance increases with V. The asymptotic large-V
behavior is \sim V/V_c (where eV_c=D/L^2 is the Thouless energy),
in agreement with the earlier prediction by Larkin and Khmelnitskii. We find,
however, that this asymptotics has a very small numerical prefactor and sets in
at very large V/V_c only, which strongly complicates its experimental
observation. This high-voltage behavior is preceded by a crossover regime,
V/V_c \lesssim 30, where the conductance variance increases by a factor \sim 3
as compared to its value in the regime of universal conductance fluctuations
(i.e., at V->0). We further analyze the effect of dephasing due to the
electron-electron scattering on at high voltages. With the Coulomb
interaction taken into account, the amplitude of conductance fluctuations
becomes a non-monotonic function of V. Specifically, drops as 1/V
for voltages V >> gV_c, where g is the dimensionless conductance. In this
regime, the conductance fluctuations are dominated by quantum-coherent regions
of the wire adjacent to the reservoirs.Comment: 14 pages, 4 figures. Fig.2 and one more appendix added, accepted for
publication in PR
Interaction correction to the conductance of a ballistic conductor
In disordered metals, electron-electron interactions are the origin of a
small correction to the conductivity, the "Altshuler-Aronov correction". Here
we investigate the Altshuler-Aronov correction of a conductor in which the
electron motion is ballistic and chaotic. We consider the case of a double
quantum dot, which is the simplest example of a ballistic conductor in which
the Altshuler-Aronov correction is nonzero. The fact that the electron motion
is ballistic leads to an exponential suppression of the correction if the
Ehrenfest time is larger than the mean dwell time or the inverse temperature.Comment: 4 pages, 2 figure
Crossover from diffusive to strongly localized regime in two-dimensional systems
We have studied the conductance distribution function of two-dimensional
disordered noninteracting systems in the crossover regime between the diffusive
and the localized phases. The distribution is entirely determined by the mean
conductance, g, in agreement with the strong version of the single-parameter
scaling hypothesis. The distribution seems to change drastically at a critical
value very close to one. For conductances larger than this critical value, the
distribution is roughly Gaussian while for smaller values it resembles a
log-normal distribution. The two distributions match at the critical point with
an often appreciable change in behavior. This matching implies a jump in the
first derivative of the distribution which does not seem to disappear as system
size increases. We have also studied 1/g corrections to the skewness to
quantify the deviation of the distribution from a Gaussian function in the
diffusive regime.Comment: 4 pages, 4 figure
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