Interaction corrections to the Hall coefficient at intermediate temperatures

We investigate the effect of electron-electron interaction on the temperature dependence of the Hall coefficient of 2D electron gas at arbitrary relation between the temperature $T$ and the elastic mean-free time $\tau$. At small temperature $T\tau \ll \hbar$ we reproduce the known relation between the logarithmic temperature dependences of the Hall coefficient and of the longitudinal conductivity. At higher temperatures, this relation is violated quite rapidly; correction to the Hall coefficient becomes $\propto 1/T$ whereas the longitudinal conductivity becomes linear in temperature.Comment: 4 pages, 3 .eps figure

Crossover from Poisson to Wigner-Dyson Level Statistics in Spin Chains with Integrability Breaking

We study numerically the evolution of energy-level statistics as an integrability-breaking term is added to the XXZ Hamiltonian. For finite-length chains, physical properties exhibit a cross-over from behavior resulting from the Poisson level statistics characteristic of integrable models to behavior corresponding to the Wigner-Dyson statistics characteristic of the random-matrix theory used to describe chaotic systems. Different measures of the level statistics are observed to follow different crossover patterns. The range of numerically accessible system sizes is too small to establish with certainty the scaling with system size, but the evidence suggests that in a thermodynamically large system an infinitesimal integrability breaking would lead to Wigner-Dyson behavior.Comment: 8 pages, 8 figures, Revtex

Effects of anisotropic spin-exchange interactions in spin ladders

We investigate the effects of the Dzialoshinskii-Moriya (DM) and Kaplan-Shekhtman-Entin-Wohlman-Aharony (KSEA) interactions on various thermodynamic and magnetic properties of a spin 1/2 ladder. Using the Majorana fermion representation, we derive the spectrum of low energy excitations for a pure DM interaction and in presence of a superimposed KSEA interaction. We calculate the various correlation functions for both cases and discuss how they are modified with respect to the case of an isotropic ladder. We also discuss the electron spin resonance (ESR) spectrum of the system and show that it is strongly influenced by the orientation of the magnetic field with respect to the Dzialoshinskii-Moriya vector. Implications of our calculations for NMR and ESR experiments on ladder systems are discussed.Comment: 14 pages, 4 eps figures, corrected calculation of NMR rate (v3

Interaction corrections at intermediate temperatures: dephasing time

We calculate the temperature dependence of the weak localization correction in a two dimensional system at arbitrary relation between temperature, $T$ and the elastic mean free time. We describe the crossover in the dephasing time ${\tau_\phi(T)}$ between the high temperature, $1/\tau_\phi \simeq T^2 \ln T$, and the low temperature $1/\tau_\phi \simeq T$ behaviors. The prefactors in these dependences are not universal, but are determined by the Fermi liquid constant characterising the spin exchange interaction.Comment: 4 pages, to appear in PRB, minor errors corrected, added reference

Finite size effects on transport coefficients for models of atomic wires coupled to phonons

We consider models of quasi-1-d, planar atomic wires consisting of several, laterally coupled rows of atoms, with mutually non-interacting electrons. This electronic wire system is coupled to phonons, corresponding, e.g., to some substrate. We aim at computing diffusion coefficients in dependence on the wire widths and the lateral coupling. To this end we firstly construct a numerically manageable linear collision term for the dynamics of the electronic occupation numbers by following a certain projection operator approach. By means of this collision term we set up a linear Boltzmann equation. A formula for extracting diffusion coefficients from such Boltzmann equations is given. We find in the regime of a few atomic rows and intermediate lateral coupling a significant and non-trivial dependence of the diffusion coefficient on both, the width and the lateral coupling. These results, in principle, suggest the possible applicability of such atomic wires as electronic devices, such as, e.g., switches.Comment: 9 pages, 5 figures, accepted for publication in Eur. Phys. J.

Mesoscopic fluctuations of Coulomb drag between quasi-ballistic 1D-wires

Quasiballistic 1D quantum wires are known to have a conductance of the order of 2e^2/h, with small sample-to-sample fluctuations. We present a study of the transconductance G_12 of two Coulomb-coupled quasiballistic wires, i.e., we consider the Coulomb drag geometry. We show that the fluctuations in G_12 differ dramatically from those of the diagonal conductance G_ii: the fluctuations are large, and can even exceed the mean value, thus implying a possible reversal of the induced drag current. We report extensive numerical simulations elucidating the fluctuations, both for correlated and uncorrelated disorder. We also present analytic arguments, which fully account for the trends observed numerically.Comment: 10 pages including 7 figures. Minor changes according to referee report. Accepted for PR

Spin magnetization of strongly correlated electron gas confined in a two-dimensional finite lattice

The influence of disorder and interaction on the ground state polarization of the two-dimensional (2D) correlated electron gas is studied by numerical investigations of unrestricted Hartree-Fock equations. The ferromagnetic ground state is found to be plausible when the electron number is lowered and the interaction and disorder parameters are suitably chosen. For a finite system at constant electronic density the disorder induced spin polarization is cut off when the electron orbitals become strongly localized to the individual network sites. The fluctuations of the interaction matrix elements are calculated and brought out as favoring the ferromagnetic instability in the extended and weak localization regime. The localization effect of the Hubbard interaction term is discussed.Comment: 7 pages, 9 figure

Nondissipative Drag Conductance as a Topological Quantum Number

We show in this paper that the boundary condition averaged nondissipative drag conductance of two coupled mesoscopic rings with no tunneling, evaluated in a particular many-particle eigenstate, is a topological invariant characterized by a Chern integer. Physical implications of this observation are discussed.Comment: 4 pages, no figure. Title modified and significant revision made to the text. Final version appeared in PR

Electrons in an annealed environment: A special case of the interacting electron problem

The problem of noninteracting electrons in the presence of annealed magnetic disorder, in addition to nonmagnetic quenched disorder, is considered. It is shown that the proper physical interpretation of this model is one of electrons interacting via a potential that is long-ranged in time, and that its technical analysis by means of renormalization group techniques must also be done in analogy to the interacting problem. As a result, and contrary to previous claims, the model does not simply describe a metal-insulator transition in $d=2+\epsilon$ ($\epsilon\ll 1$) dimensions. Rather, it describes a transition to a ferromagnetic state that, as a function of the disorder, precedes the metal-insulator transition close to $d=2$. In $d=3$, a transition from a paramagnetic metal to a paramagnetic insulator is possible.Comment: 13 pp., LaTeX, 2 eps figs; final version as publishe

Sign-reversal of drag in bilayer systems with in-plane periodic potential modulation

We develop a theory for describing frictional drag in bilayer systems with in-plane periodic potential modulations, and use it to investigate the drag between bilayer systems in which one of the layers is modulated in one direction. At low temperatures, as the density of carriers in the modulated layer is changed, we show that the transresistivity component in the direction of modulation can change its sign. We also give a physical explanation for this behavior.Comment: 4 pages, 4 figure