64 research outputs found
Conductivity in a disordered one-dimensional system of interacting fermions
Dynamical conductivity in a disordered one-dimensional model of interacting
fermions is studied numerically at high temperatures and in the
weak-interaction regime in order to find a signature of many-body localization
and vanishing d.c. transport coefficients. On the contrary, we find in the
regime of moderately strong local disorder that the d.c. conductivity sigma0
scales linearly with the interaction strength while being exponentially
dependent on the disorder. According to the behavior of the charge stiffness
evaluated at the fixed number of particles, the absence of the many-body
localization seems related to an increase of the effective localization length
with the interaction.Comment: 4 pages, 5 figures, submitted to PR
Quantum adiabatic polarons by translationally invariant perturbation theory
The translationally invariant diagrammatic quantum perturbation theory (TPT)
is applied to the polaron problem on the 1D lattice, modeled through the
Holstein Hamiltonian with the phonon frequency omega0, the electron hopping t
and the electron-phonon coupling constant g. The self-energy diagrams of the
fourth-order in g are calculated exactly for an intermittently added electron,
in addition to the previously known second-order term. The corresponding
quadratic and quartic corrections to the polaron ground state energy become
comparable at t/omega0>1 for g/omega0~(t/omega0)^{1/4} when the electron
self-trapping and translation become adiabatic. The corresponding non
adiabatic/adiabatic crossover occurs while the polaron width is large, i.e. the
lattice coarsening negligible. This result is extended to the range
(t/omega0)^{1/2}>g/omega0>(t/omega0)^{1/4}>1 by considering the scaling
properties of the high-order self-energy diagrams. It is shown that the polaron
ground state energy, its width and the effective mass agree with the results
found traditionally from the broken symmetry side, kinematic corrections
included. The Landau self trapping of the electron in the classic
self-consistent, localized displacement potential, the restoration of the
translational symmetry by the classic translational Goldstone mode and the
quantization of the polaronic translational coordinate are thus all encompassed
by a quantum theory which is translationally invariant from the outset.Comment: 10 pages, 5 figure
Thermal transport in a spin-1/2 Heisenberg chain coupled to a (non) magnetic impurity
We explore the effect of a (non) magnetic impurity on the thermal transport
of the spin-1/2 Heisenberg chain model. This unique system allows to probe
Kondo-type phenomena in a prototype strongly correlated system. Using numerical
diagonalization techniques we study the scaling of the frequency dependent
thermal conductivity with system size and host-impurity coupling strength as
well as the dependence on temperature. We focus in particular on the analysis
of cutting-healing of weak links or a magnetic impurity by the host chain via
Kondo-like screening as the temperature is lowered.Comment: 7 pages, 12 figure
Exact solution of electronic transport in semiconductors dominated by scattering on polaronic impurities
The scattering of electrons on impurities with internal degrees of freedom is
bound to produce the signatures of the scatterer's own dynamics and results in
nontrivial electronic transport properties. Previous studies of polaronic
impurities in low-dimensional structures, like molecular junctions and
one-dimensional nanowire models, have shown that perturbative treatments cannot
account for a complex energy dependence of the scattering cross section in such
systems. Here we derive the exact solution of polaronic impurities shaping the
electronic transport in bulk (3D) systems. In the model with a short-ranged
electron-phonon interaction, we solve for and sum over all elastic and
inelastic partial cross sections, abundant in resonant features. The
temperature dependence of the charge mobility shows the power-law dependence,
, with being highly sensitive to impurity
parameters. The latter may explain nonuniversal power-law exponents observed
experimentally, e.g. in high-quality organic molecular semiconductors.Comment: 5 pages, 6 figure
Short-time dynamics in the 1D long-range Potts model
We present numerical investigations of the short-time dynamics at criticality
in the 1D Potts model with power-law decaying interactions of the form
1/r^{1+sigma}. The scaling properties of the magnetization, autocorrelation
function and time correlations of the magnetization are studied. The dynamical
critical exponents theta' and z are derived in the cases q=2 and q=3 for
several values of the parameter belonging to the nontrivial critical
regime.Comment: 8 pages, 8 figures, minor changes - several typos fixed, one
reference change
Calculation of excited polaron states in the Holstein model
An exact diagonalization technique is used to investigate the low-lying
excited polaron states in the Holstein model for the infinite one-dimensional
lattice. For moderate values of the adiabatic ratio, a new and comprehensive
picture, involving three excited (coherent) polaron bands below the phonon
threshold, is obtained. The coherent contribution of the excited states to both
the single-electron spectral density and the optical conductivity is evaluated
and, due to the invariance of the Hamiltonian under the space inversion, the
two are shown to contain complementary information about the single-electron
system at zero temperature. The chosen method reveals the connection between
the excited bands and the renormalized local phonon excitations of the
adiabatic theory, as well as the regime of parameters for which the electron
self-energy has notable non-local contributions. Finally, it is shown that the
hybridization of two polaron states allows a simple description of the ground
and first excited state in the crossover regime.Comment: 12 pages, 9 figures, submitted to PR
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