4,347 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
Spin noise spectroscopy in GaAs
We observe the noise spectrum of electron spins in bulk GaAs by Faraday
rotation noise spectroscopy. The experimental technique enables the undisturbed
measurement of the electron spin dynamics in semiconductors. We measure
exemplarily the electron spin relaxation time and the electron Lande g-factor
in n-doped GaAs at low temperatures and find good agreement of the measured
noise spectrum with an unpretentious theory based on Poisson distribution
probability.Comment: 4 pages, 4 figure
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
Development and fabrication of bismaleimide-graphite composites
The successful fabrication of high temperature resistant composites depends mainly on the processability of the resin binder matrix. For two new bismaleimide type resins the processing of graphite fabric prepregs to composites is described. One resin coded M 751 has to be processed from N-Methylpyrrolidone, the other resin evaluated is a so-called hot melt solvent-less system. Commercial T300/3000 Graphite fabrics were used as reinforcement. The M 751 - Resin is a press grade material and laminates are therefore moulded in high pressure conditions (400 N/sq cm). The solvent-less resin system H 795 is an autoclave grade material and can be cured at 40 N/sq cm. The cure cycles for both the press grade and the autoclave grade material (Fiberite W 143 fabric prepregs) are provided and the mechanical properties of laminates at low (23 C) and high (232 C) temperatures were measured. For comparison, the neat resin flexural properties are also presented. The water absorption for the neat resins and the graphite fabric laminates after a 1000 hour period was evaluated
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
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