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I. L. Aleiner

Publications and source records attributed to I. L. Aleiner.

88 records · Page 5Linked to original sources
arXiv1998

Domain walls and the conductivity of mesoscopic ferromagnets

Quantum interference phenomena in the conductivity of mesoscopic ferromagnets are considered, particularly with regard to the effects of geometric phases acquired by electrons propagating through regions of spatially varying magnetization (due, e.g., to magnetic domain walls). Weak localization and electron-electron interaction quantum corrections to the conductivity and universal conductance fluctuations are discussed. Experiments are proposed for multiply-connected geometries that should reveal conductance oscillations with variations of the profile of the magnetization.

cond-mat.mes-hall↗
arXiv1997

Shifts of Random Energy Levels by a Local Perturbation

We consider the effect of a local perturbation on the energy levels of a system described by random matrix theory. An analytic expression for the joint distribution function of initial and final energy levels is obtained. In the case of unitary ensemble we also find the two-point correlation function of initial and final densities of states.

cond-mat.mes-hall↗
arXiv1997

Mesoscopic charge quantization

We study the Coulomb blockade in a chaotic quantum dot connected to a lead by a single channel at nearly perfect transmission. We take into account quantum fluctuations of the dot charge and a finite level spacing for electron states within the dot. Mesoscopic fluctuations of thermodynamic and transport properties in the Coulomb blockade regime exist at any transmission coefficient. In contrast to the previous theories, we show that by virtue of these mesoscopic fluctuations, the Coulomb blockade is not destroyed completely even at perfect transmission. The oscillatory dependence of all the observable characteristics on the gate voltage is preserved, its period is still defined by the charge of a single electron. However, phases of those oscillations are random; because of the randomness, the Coulomb blockade shows up not in the averages but in the correlation functions of the fluctuating observables (e.g., capacitance or tunneling conductance). This phenomenon may be called "mesoscopic charge quantization".

cond-mat.mes-hall↗
arXiv1997

Tunneling Anomaly in Superconductor above Paramagnetic Limit

We study the tunneling density of states (DoS) in the superconducting systems driven by Zeeman splitting E_Z into the paramagnetic phase. We show that, even though the BCS gap disappears, superconducting fluctuations cause a strong DoS singularity in the vicinity of energies -E^* for electrons polarized along the magnetic field and E^* for the opposite polarization. The position of the singularity E^*=(1/2) (E_Z + \sqrt{E_Z^2- Δ^2}) (where Δis BCS gap at E_Z=0) is universal. We found analytically the shape of the DoS for different dimensionality of the system. For ultrasmall grains the singularity has the form of the hard gap, while in higher dimensions it appears as a significant though finite dip. Our results are consistent with recent experiments in superconducting films.

cond-mat.supr-con↗
arXiv1997

Dephasing and the Orthogonality Catastrophe in Tunneling through a Quantum Dot: the ``Which Path?'' Interferometer

The ``Which Path?'' interferometer consists of an Aharonov-Bohm ring with a quantum dot (QD) built in one of its arms, and an additional quantum point contact (QPC) located close to the QD. The transmission coefficient of the QPC depends on the charge state of the QD. Hence the point contact causes controllable dephasing of transport through the QD, and acts as a measurement device for which path an electron takes through the ring. We calculate the suppression of the Aharonov-Bohm oscillations which is caused both by dephasing and by the orthogonality catastrophe, i.e., respectively, by real and virtual electron-hole pair creation at the QPC.

cond-mat.mes-hall↗
arXiv1996

Quantum Coulomb Blockade in Chaotic Systems

We study the Coulomb blockade in a chaotic cavity connected to a lead by a perfectly transmitting quantum channel. In contrast to the previous theories, we show that the quantum fluctuations of charge, resulting from the perfect transmission, do not destroy the Coulomb blockade completely. The oscillatory dependence of all the observable characteristics on the gate voltage persists, its period is not affected; however, phases of the oscillations are random, reflecting the chaotic electron motion in the cavity. Because of this randomness, the Coulomb blockade shows up not in the averages but in the correlation functions of the fluctuating observables (e.g., capacitance or tunneling conductance).

cond-mat.mes-hall↗
arXiv1996

Divergence of the Classical trajectories and Weak Localization

We study the weak localization correction (WLC) to transport coefficients of a system of electrons in a static long-range potential (e.g. an antidot array or ballistic cavity). We found that the weak localization correction to the current response is delayed by the large time $t_E = λ^{-1} |\ln \hbar|$, where $λ$ is the Lyapunov exponent. In the semiclassical regime $t_E$ is much larger than the transport lifetime. Thus, the fundamental characteristic of the classical chaotic motion, Lyapunov exponent, may be found by measuring the frequency or temperature dependence of WLC.

cond-mat↗
arXiv1996

Role of divergence of classical trajectories in quantum chaos

We study logarithmical in $\hbar$ effects in the statistical description of quantum chaos. We found analytical expressions for the deviations from the universality in the weak localization corrections and the level statistics and showed that the characteristic scale for these deviations is the Ehrenfest time, $t_E= λ^{-1}|\ln\hbar|$, where $λ$ is the Lyapunov exponent of the classical motion.

cond-mat↗
arXiv1996

Mesoscopic Fluctuations of Elastic Cotunneling

We study mesoscopic fluctuations of the conductance through a quantum dot at the wings of the Coulomb blokade peaks. At low temperatures, the main mechanism of conduction is the elastic cotunneling. The conductance strongly fluctuates with an applied magnetic field. The magnetic correlation field is shown to be controlled by the charging energy, and the correlation function has a universal form. The distribution function for the conductance obtained analytically shows a non-trivial crossover between the orthogonal and unitary ensembles.

cond-mat↗
arXiv1996

Tunneling ``zero-bias'' anomaly in the quasi-ballistic regime

For the first time, we study the tunneling density of states (DOS) of the interacting electron gas beyond the diffusive limit. A strong correction to the DOS persists even at electron energies exceeding the inverse transport relaxation time, which could not be expected from the well-known Altshuler-Aronov-Lee (AAL) theory. This correction originates from the interference between the electron waves scattered by an impurity and by the Friedel oscillation this impurity creates. Account for such processes also revises the AAL formula for the DOS in the diffusive limit.

cond-mat↗
arXiv1996

Theory of Andreev reflection in a junction with a strongly disordered semiconductor

We study the conduction of a {\sl N~-~Sm~-~S} junction, where {\sl Sm} is a strongly disordered semiconductor. The differential conductance $dI/dV$ of this {\sl N~-~Sm~-~S} structure is predicted to have a sharp peak at $V=0$. Unlike the case of a weakly disordered system, this feature persists even in the absence of an additional (Schottky) barrier on the boundary. The zero-bias conductance of such a junction $G_{NS}$ is smaller only by a numerical factor than the conductance in the normal state $G_N$. Implications for experiments on gated heterostructures with superconducting leads are discussed.

cond-mat↗
arXiv1995

Two - Dimensional Electron Liquid in a Weak Magnetic Field

We present an effective theory describing the low-energy properties of an interacting 2D electron gas at large non-integer filling factors $ν\gg 1$. Assuming that the interaction is sufficiently weak, $r_s < 1$, we integrate out all the fast degrees of freedom, and derive the effective Hamiltonian acting in the Fock space of the partially filled Landau level only. This theory enables us to find two energy scales controlling the electron dynamics at energies less than $\hbarω_c$. The first energy scale, $(\hbarω_c/ν)\ln\left(νr_s\right)$, appears in the one electron spectral density as the width of a pseudogap. The second scale, $r_s\hbarω_c$, is parametrically larger; it characterizes the exchange-enhanced spin splitting and the thermodynamic density of states.

cond-mat↗
arXiv1994

Tunneling into a Two-Dimensional Electron Liquid in a Weak Magnetic Field

We study the spectral density function of a two-dimensional electron liquid in a weak magnetic field, the filling factor $ν\gg 1$. A hydrodynamic model for low-energy excitations of the liquid is developed. It is found that even at $ν\gg 1$ the density of states exhibits a gap at low energies. Its width $2E_0$ depends on the strength of interaction only logarithmically, $2E_0=(\hbarω_c/ν)\ln (νe^2/\varepsilon\hbar v_F)$. The effects of temperature and disorder on the density of states are discussed.

cond-mat↗
arXiv1993

Effect of screening of the Coulomb interaction on the conductivity in the quantum Hall regime

We study variable range hopping in the quantum Hall effect regime in the presence of a metallic gate parallel to the plane of a two-dimensional electron gas. Screening of the Coulomb interaction by the gate causes the partial ``filling'' of the Coulomb gap in the density of localized states. At low enough temperatures this leads to a substantial enhancement and a new temperature behavior of the hopping conductivity. As a result, the diagonal conductivity peaks become much wider. The power law dependence of the width of the peaks on the temperature changes: the corresponding exponent turns out to be twice as small as that for gateless structures. The width dependences on the current in non-ohmic regime and on the frequency for the absorption of the electromagnetic waves experience a similar modification. The experimental observation of the crossovers predicted may demonstrate the important role of the Coulomb interaction in the integer quantum Hall regime.

cond-mat↗
arXiv1993

Novel Edge Excitations of Two-dimensional Electron Liquid in a Magnetic Field

We investigate the low-energy spectrum of excitations of a compressible electron liquid in a strong magnetic field. These excitations are localized at the periphery of the system. The analysis of a realistic model of a smooth edge yields new branches of acoustic excitation spectrum in addition to the well known edge magnetoplasmon mode. The velocities are found and the observability conditions are established for the new modes.

cond-mat↗