h/2eh/2e--Oscillations for Correlated Electron Pairs in Disordered Mesoscopic Rings

The full spectrum of two interacting electrons in a disordered mesoscopic one--dimensional ring threaded by a magnetic flux is calculated numerically. For ring sizes far exceeding the one--particle localization length $L_1$ we find several $h/2e$--periodic states whose eigenfunctions exhibit a pairing effect. This represents the first direct observation of interaction--assisted coherent pair propagation, the pair being delocalized on the scale of the whole ring.Comment: 4 pages, uuencoded PostScript, containing 5 figures

Mesoscopic Luttinger Liquid Theory in an Aharonov-Bohm Ring

A careful study on the mesoscopic PC in a Luttinger liquid ring is carried out. It is shown that discreteness plays an important role in calculating the PC caused by the magnetic flux. At zero temperature, the current is shown to be independent of the interaction even when $g=g_2-g_4$ is not zero. The current becomes enhanced at finite temperatures comparing to the non-interacting case, when the parameter g is positive.Comment: 4 pages, 2 figures. Version to appear in PR

Spin and interaction effects on charge distribution and currents in one-dimensional conductors and rings within the Hartree-Fock approximation

Using the self--consistent Hartree-Fock approximation for electrons with spin at zero temperature, we study the effect of the electronic interactions on the charge distribution in a one-dimensional continuous ring containing a single $\delta$ scatterer. We reestablish that the interaction suppresses the decay of the Friedel oscillations. Based on this result, we show that in an infinite one dimensional conductor containing a weak scatterer, the current is totally suppressed because of a gap opened at the Fermi energy. In a canonical ensemble of continuous rings containing many scatterers, the interactions enhance the average and the typical persistent current.Comment: 5 pages, 4 figure

Analytical Results for Random Band Matrices with Preferential Basis

Using the supersymmetry method we analytically calculate the local density of states, the localiztion length, the generalized inverse participation ratios, and the distribution function of eigenvector components for the superposition of a random band matrix with a strongly fluctuating diagonal matrix. In this way we extend previously known results for ordinary band matrices to the class of random band matrices with preferential basis. Our analytical results are in good agreement with (but more general than) recent numerical findings by Jacquod and Shepelyansky.Comment: 8 pages RevTex and 1 Figure, both uuencode

Persistent Currents in 1D Disordered Rings of Interacting Electrons

We calculate the persistent current of 1D rings of spinless fermions with short-range interactions on a lattice with up to 20 sites, and in the presence of disorder, for various band fillings. We find that {\it both} disorder and interactions always decrease the persistent current by localizing the electrons. Away from half-filling, the interaction has a much stronger influence in the presence of disorder than in the pure case.Comment: Latex file, 11 pages, 5 figures available on request, Report LPQTH-93/1

Conductance length autocorrelation in quasi one-dimensional disordered wires

Employing techniques recently developed in the context of the Fokker--Planck approach to electron transport in disordered systems we calculate the conductance length correlation function $$ for quasi 1d wires. Our result is valid for arbitrary lengths L and $\Delta L$. In the metallic limit the correlation function is given by a squared Lorentzian. In the localized regime it decays exponentially in both L and $\Delta L$. The correlation length is proportional to L in the metallic regime and saturates at a value approximately given by the localization length $\xi$ as $L\gg\xi$.Comment: 23 pages, Revtex, two figure

Electron-electron interactions in one- and three-dimensional mesoscopic disordered rings: a perturbative approach

We have computed persistent currents in a disordered mesoscopic ring in the presence of small electron-electron interactions, treated in first order perturbation theory. We have investigated both a contact (Hubbard) and a nearest neighbour interaction in 1D and 3D. Our results show that a repulsive Hubbard interaction produces a paramagnetic contribution to the average current (whatever the dimension) and increases the value of the typical current. On the other hand, a nearest neighbour repulsive interaction results in a diamagnetic contribution in 1D and paramagnetic one in 3D, and tends to decrease the value of the typical current in any dimension. Our study is based on numerical simulations on the Anderson model and is justified analytically in the presence of very weak disorder. We have also investigated the influence of the amount of disorder and of the statistical (canonical or grand-canonical) ensemble.Comment: 7 pages in REVTEX, 4 figure

The interplay between electron-electron interactions and impurities in one-dimensional rings

The persistent current and charge stiffness of a one-dimensional Luttinger liquid on a ring threaded by a magnetic flux are calculated by Monte Carlo simulation. By changing the random impurity potential strength and the electron-electron interaction, we see a crossover behavior between weak and strong impurity limits. For weak impurity potentials, interactions enhance impurity effects, that is, interactions decrease the current and the stiffness. On the other hand, interactions tend to screen impurities when the impurity potential is strong. Temperature dependence of the persistent current and the charge stiffness shows a peak at a characteristic temperature, consistent with a recent single impurity study.Comment: 4 pages (ReVTeX3.0) + 3 figures (in uuencoded postscript format) appended in the end of the fil

Enhanced Charge and Spin Currents in the One-Dimensional Disordered Mesoscopic Hubbard Ring

We consider a one-dimensional mesoscopic Hubbard ring with and without disorder and compute charge and spin stiffness as a measure of the permanent currents. For finite disorder we identify critical disorder strength beyond which the charge currents in a system with repulsive interactions are {\em larger} than those for a free system. The spin currents in the disordered repulsive Hubbard model are enhanced only for small $U$, where the magnetic state of the system corresponds to a charge density wave pinned to the impurities. For large $U$, the state of the system corresponds to localized isolated spins and the spin currents are found to be suppressed. For the attractive Hubbard model we find that the charge currents are always suppressed compared to the free system at all length scales.Comment: 20 RevTeX 3.0 pages, 8 figures NOT include

Spin-twist driven persistent current in a strongly correlated two-dimensional electron system: a manifestation of the gauge field

A persistent current, coupled with the spin state, of purely many-body origin is shown to exist in Nagaoka's ferromagnetic state in two dimensions (2D). This we regard as a manifestation of a gauge field, which comes from the surrounding spin configuration and acts on the hole motion, being coupled to the Aharonov-Bohm flux. This provides an example where the electron-electron interaction exerts a profound effect involving the spins in clean two-dimensional lattice systems in sharp contrast to continuum or spinless fermion systems.Comment: 11 pages, typeset using Revtex 3.0, Phys. Rev. B in press, 2 figures available upon request at [email protected]