30 research outputs found
Quantum Transport in Strongly Correlated Systems:A Density Matrix Renormalization Group Study
Strong enhancement of transport by interaction on contact links
Strong repulsive interactions within a one dimensional Fermi system in a
two-probe configuration normally lead to a reduced off-resonance conductance.
We show that if the repulsive interaction extends to the contact regions, a
strong increase of the conductance may occur, even for systems where one would
expect to find a reduced conductance. An essential ingredient in our
calculations is a momentum-space representation of the leads, which allows a
high energy resolution. Further, we demonstrate that these results are
independent of the high-energy cutoff and that the relevant scale is set by the
Fermi velocity.Comment: Published version -- references correcte
Geometry of intensive scalar dissipation events in turbulence
Maxima of the scalar dissipation rate in turbulence appear in form of sheets
and correspond to the potentially most intensive scalar mixing events. Their
cross-section extension determines a locally varying diffusion scale of the
mixing process and extends the classical Batchelor picture of one mean
diffusion scale. The distribution of the local diffusion scales is analysed for
different Reynolds and Schmidt numbers with a fast multiscale technique applied
to very high-resolution simulation data. The scales take always values across
the whole Batchelor range and beyond. Furthermore, their distribution is traced
back to the distribution of the contractive short-time Lyapunov exponent of the
flow.Comment: 4 pages, 5 Postscript figures (2 with reduced quality
Chemical turbulence equivalent to Nikolavskii turbulence
We find evidence that a certain class of reaction-diffusion systems can
exhibit chemical turbulence equivalent to Nikolaevskii turbulence. The
distinctive characteristic of this type of turbulence is that it results from
the interaction of weakly stable long-wavelength modes and unstable
short-wavelength modes. We indirectly study this class of reaction-diffusion
systems by considering an extended complex Ginzburg-Landau (CGL) equation that
was previously derived from this class of reaction-diffusion systems. First, we
show numerically that the power spectrum of this CGL equation in a particular
regime is qualitatively quite similar to that of the Nikolaevskii equation.
Then, we demonstrate that the Nikolaevskii equation can in fact be obtained
from this CGL equation through a phase reduction procedure applied in the
neighborhood of a codimension-two Turing--Benjamin-Feir point.Comment: 10 pages, 3 figure
Interplay between interference and Coulomb interaction in the ferromagnetic Anderson model with applied magnetic field
We study the competition between interference due to multiple single-particle
paths and Coulomb interaction in a simple model of an Anderson-like impurity
with local-magnetic-field-induced level splitting coupled to ferromagnetic
leads. The model along with its potential experimental relevance in the field
of spintronics serves as a nontrivial benchmark system where various quantum
transport approaches can be tested and compared. We present results for the
linear conductance obtained by a spin-dependent implementation of the density
matrix renormalization group scheme which are compared with a mean-field
solution as well as a seemingly more advanced Hubbard-I approximation. We
explain why mean-field yields nearly perfect results, while the more
sophisticated Hubbard-I approach fails, even at a purely conceptual level since
it breaks hermiticity of the related density matrix. Furthermore, we study
finite bias transport through the impurity by the mean-field approach and
recently developed higher-order density matrix equations. We find that the
mean-field solution fails to describe the plausible results of the higher-order
density matrix approach both quantitatively and qualitatively as it does not
capture some essential features of the current-voltage characteristics such as
negative differential conductance