3,957 research outputs found
Transport properties near the Anderson transition
The electronic transport properties in the presence of a temperature gradient
in disordered systems near the metal-insulator transition [MIT] are considered.
The d.c. conductivity , the thermoelectric power , the thermal
conductivity and the Lorenz number are calculated for the
three-dimensional Anderson model of localization using the
Chester-Thellung-Kubo-Greenwood formulation of linear response. We show that
, S, K and can be scaled to one-parameter scaling curves with a
single scaling paramter .Comment: 4 pages, 4 EPS figures, uses annalen.cls style [included]; presented
at Localization 1999, to appear in Annalen der Physik [supplement
Phase diagram of the three-dimensional Anderson model of localization with random hopping
We examine the localization properties of the three-dimensional (3D) Anderson
Hamiltonian with off-diagonal disorder using the transfer-matrix method (TMM)
and finite-size scaling (FSS). The nearest-neighbor hopping elements are chosen
randomly according to . We find that the
off-diagonal disorder is not strong enough to localize all states in the
spectrum in contradistinction to the usual case of diagonal disorder. Thus for
any off-diagonal disorder, there exist extended states and, consequently, the
TMM converges very slowly. From the TMM results we compute critical exponents
of the metal-insulator transitions (MIT), the mobility edge , and study
the energy-disorder phase diagram.Comment: 4 pages, 5 EPS figures, uses annalen.cls style [included]; presented
at Localization 1999, to appear in Annalen der Physik [supplement
Thermoelectric Transport Properties in Disordered Systems Near the Anderson Transition
We study the thermoelectric transport properties in the three-dimensional
Anderson model of localization near the metal-insulator transition [MIT]. In
particular, we investigate the dependence of the thermoelectric power S, the
thermal conductivity K, and the Lorenz number L_0 on temperature T. We first
calculate the T dependence of the chemical potential from the number density of
electrons at the MIT using averaged density of state obtained by
diagonalization. Without any additional approximation, we determine from the
chemical potential the behavior of S, K and L_0 at low T as the MIT is
approached. We find that the d.c. conductivity and K decrease to zero at the
MIT as T -> 0 and show that S does not diverge. Both S and L_0 become
temperature independent at the MIT and depend only on the critical behavior of
the conductivity.Comment: 11 pages, 10 eps figures, coded with the EPJ macro package, submitted
to EPJ
Integrable impurities for an open fermion chain
Employing the graded versions of the Yang-Baxter equation and the reflection
equations, we construct two kinds of integrable impurities for a small-polaron
model with general open boundary conditions: (a) we shift the spectral
parameter of the local Lax operator at arbitrary sites in the bulk, and (b) we
embed the impurity fermion vertex at each boundary of the chain. The
Hamiltonians with different types of impurity terms are given explicitly. The
Bethe ansatz equations, as well as the eigenvalues of the Hamiltonians, are
constructed by means of the quantum inverse scattering method. In addition, we
discuss the ground-state properties in the thermodynamic limit.Comment: 20 pages, 4 figure
Non-equilibrium transport through a disordered molecular nanowire
We investigate the non-equilibrium transport properties of a disordered
molecular nanowire. The nanowire is regarded as a quasi-one-dimensional organic
crystal composed of self-assembled molecules. One orbital and a single random
energy are assigned to each molecule while the intermolecular coupling does not
fluctuate. Consequently, electronic states are expected to be spatially
localized. We consider the regime of strong localization, namely, the
localization length is smaller than the length of the molecular wire.
Electron-vibron interaction, taking place in each single molecule, is also
taken into account. We investigate the interplay between disorder and
electron-vibron interaction in response to either an applied electric bias or a
temperature gradient. To this end, we calculate the electric and heat currents
when the nanowire is connected to leads, using the Keldysh non-equilibrium
Green's function formalism. At intermediate temperature, scattering by disorder
dominates both charge and heat transport. We find that the electron-vibron
interaction enhances the effect of the disorder on the transport properties due
to the exponential suppression of tunneling
The Anderson model of localization: a challenge for modern eigenvalue methods
We present a comparative study of the application of modern eigenvalue
algorithms to an eigenvalue problem arising in quantum physics, namely, the
computation of a few interior eigenvalues and their associated eigenvectors for
the large, sparse, real, symmetric, and indefinite matrices of the Anderson
model of localization. We compare the Lanczos algorithm in the 1987
implementation of Cullum and Willoughby with the implicitly restarted Arnoldi
method coupled with polynomial and several shift-and-invert convergence
accelerators as well as with a sparse hybrid tridiagonalization method. We
demonstrate that for our problem the Lanczos implementation is faster and more
memory efficient than the other approaches. This seemingly innocuous problem
presents a major challenge for all modern eigenvalue algorithms.Comment: 16 LaTeX pages with 3 figures include
Lattice thermal conductivity of graphene nanostructures
Non-equilibrium molecular dynamics is used to investigate the heat current
due to the atomic lattice vibrations in graphene nanoribbons and nanorings
under a thermal gradient. We consider a wide range of temperature, nanoribbon
widths up to 6nm and the effect of moderate edge disorder. We find that narrow
graphene nanorings can efficiently suppress the lattice thermal conductivity at
low temperatures (~100K), as compared to nanoribbons of the same width.
Remarkably, rough edges do not appear to have a large impact on lattice energy
transport through graphene nanorings while nanoribbons seem more affected by
imperfections. Furthermore, we demonstrate that the effects of
hydrogen-saturated edges can be neglected in these graphene nanostructures
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