9 research outputs found
Symmetry broken motion of a periodically driven Brownian particle: nonadiabatic regime
We report a theoretical study of an overdamped Brownian particle dynamics in
the presence of both a spatially modulated one-dimensional periodic potential
and a periodic alternating force (AF). As the periodic potential has a low
symmetry (a ratchet potential) the Brownian particle displays a broken symmetry
motion with a nonzero time average velocity. By making use of the Green
function method and a mapping to the theory of Brillouin bands the probability
distribution of the particle coordinate is derived and the nonlinear dependence
of the macroscopic velocity on the frequency and the amplitude of AF is found.
In particular, our theory allows to go beyond the adiabatic limit and to
explain the peculiar reversal of the velocity sign found previously in the
numerical analysis.Comment: 4 pages, 2 figure
Coulomb blockade in metallic grains at large conductance
We study Coulomb blockade effects in the thermodynamic quantities of a weakly
disordered metallic grain coupled to a metallic lead by a tunneling contact
with a large conductance . We consider the case of broken time-reversal
symmetry and obtain expressions for both the {\em ensemble averaged} amplitude
of the Coulomb blockade oscillations of the thermodynamic potential and the
correlator of its {\em mesoscopic fluctuations} for a finite mean level spacing
in the grain. We develop a novel method which allows for an exact
evaluation of the functional integral arising from disorder averaging. The
results and the method are applicable in the temperature range .Comment: 18 pages, 3 figures (revised version
Vortex Dynamics and the Hall-Anomaly: a Microscopic Analysis
We present a microscopic derivation of the equation of motion for a vortex in
a superconductor. A coherent view on vortex dynamics is obtained, in which {\it
both} hydrodynamics {\it and} the vortex core contribute to the forces acting
on a vortex. The competition between these two provides an interpretation of
the observed sign change in the Hall angle in superconductors with mean free
path of the order of the coherence length in terms of broken
particle-hole symmetry, which is related to details of the microscopic
mechanism of superconductivity.Comment: 12 pages, late
Coulomb gap in a model with finite charge transfer energy
The Coulomb gap in a donor-acceptor model with finite charge transfer energy
describing the electronic system on the dielectric side of the
metal-insulator transition is investigated by means of computer simulations on
two- and three-dimensional finite samples with a random distribution of equal
amounts of donor and acceptor sites. Rigorous relations reflecting the symmetry
of the model presented with respect to the exchange of donors and acceptors are
derived. In the immediate neighborhood of the Fermi energy the the
density of one-electron excitations is determined solely by
finite size effects and further away from is described by
an asymmetric power law with a non-universal exponent, depending on the
parameter .Comment: 10 pages, 6 figures, submitted to Phys. Rev.
Universal Spectral Correlations in Diffusive Quantum Systems
We have studied numerically several statistical properties of the spectra of
disordered electronic systems under the influence of an Aharonov Bohm flux
, which acts as a time--reversal symmetry breaking parameter. The
distribution of curvatures of the single electron energy levels has a modified
Lorentz form with different exponents in the GOE and GUE regime. It has
Gaussian tails in the crossover regime. The typical curvature is found to vary
as ( is the Thouless energy and
the mean level spacing) and to diverge at zero flux. We show that the harmonics
of the variation with of single level quantities (current or
curvature) are correlated, in contradiction with the perturbative result. The
single level current correlation function is found to have a logarithmic
behavior at low flux, in contrast to the pure symmetry cases. The distribution
of single level currents is non--Gaussian in the GOE--GUE transition regime. We
find a universal relation between , the typical slope of the levels, and
, the width of the curvature distribution, as was proposed by Akkermans
and Montambaux. We conjecture the validity of our results for any chaotic
quantum system.Comment: 23 pages of RevTEX, 11 figures avaiable upon request; submitted to
PRB; report number levs0