arXiv subjects

M. E. Raikh

Publications and source records attributed to M. E. Raikh.

133 records · Page 8Linked to original sources

arXiv1996

Re-entrant resonant tunneling

We study the effect of electron-electron interactions on the resonant-tunneling spectroscopy of the localized states in a barrier. Using a simple model of three localized states, we show that, due to the Coulomb interactions, a single state can give rise to two resonant peaks in the conductance as a function of gate voltage, G(Vg). We also demonstrate that an additional higher-order resonance with Vg-position in between these two peaks becomes possibile when interactions are taken into account. The corresponding resonant-tunneling process involves two-electron transitions. We have observed both these effects in GaAs transistor microstructures by studying the time evolution of three adjacent G(Vg) peaks caused by fluctuating occupation of an isolated impurity (modulator). The heights of the two stronger peaks exibit in-phase fluctuations. The phase of fluctuations of the smaller middle peak is opposite. The two stronger peaks have their origin in the same localized state, and the third one corresponds to a co-tunneling process.

cond-mat↗

arXiv1996

Short--range impurity in the vicinity of a saddle point and the levitation of the 2D delocalized states in a magnetic field

The effect of a short--range impurity on the transmission through a saddle--point potential for an electron, moving in a strong magnetic field, is studied. It is demonstrated that for a random position of an impurity and random sign of its potential the impurity--induced mixing of the Landau levels diminishes {\em on average} the transmission coefficient. This results in an upward shift (levitation) of the energy position of the delocalized state in a smooth potential. The magnitude of the shift is estimated. It increases with decreasing magnetic field $B$ as $B^{-4}$.

cond-mat↗

arXiv1995

Two-electron state in a disordered 2D island: pairing caused by the Coulomb repulsion

We show the existence of bound two-electron states in an almost depleted two-dimensional island. These two-electron states are carried by special compact configurations of four single-electron levels. The existence of these states does not require phonon mediation, and is facilitated by the disorder-induced potential relief and by the electron-electron repulsion only. The density of two-electron states is estimated and their evolution with the magnetic field is discussed.

cond-mat↗

arXiv1995

Surface plasmon in 2D Anderson insulator with interactions

We study the effect of interactions on the zero-temperature a.c. conductivity of 2D Anderson insulator at low frequencies. We show that the enhancement of the real part of conductivity due to the Coulomb correlations in the occupation numbers of localized states results in the change of the sign of imaginary part within a certain frequency range. As a result, the propagation of a surface plasmon in a localized system becomes possible. We analize the dispersion law of the plasmon for the two cases: unscreened Coulomb interactions and the interactions screened by a gate electrode spaced by some distance from the electron plane.

cond-mat↗

arXiv1995

Negative hopping magnetoresistance of two-dimensional electron gas in a smooth random potential

We show that the tunnel coupling between semiclassical states localized in different minima of a smooth random potential increases when magnetic field is applied. This increase originates from the difference in gauge factors which electron wave functions belonging to different electron ``lakes'' acquire in the presence of the field. We illustrate the increase of coupling by a model calculation of tunneling through a saddle point separating two adjacent lakes. In the common case, when the barrier between two lakes is much narrower than their size, the characteristic magnetic field is determined by the area of the lakes, and thus may be quite small. The effect of the field on coupling constants leads to a negative magnetoresistance in low-temperature conduction.

cond-mat↗

arXiv1995

Quantum Hall effect in spin-degenerate Landau levels: Spin-orbit enhancement of the conductivity

The quantum Hall regime in a smooth random potential is considered when two disorder-broadened Zeeman levels overlap strongly. Spin-orbit coupling is found to cause a drastic change in the percolation network which leads to a strong enhancement of the dissipative conductivity at finite temperature, provided the Fermi level $E_F$ lies between the energies of two delocalized states $E=\pmΔ$, $2Δ$ being the Zeeman splitting. The conductivity is shown to exhibit a box-like behavior with changing magnetic field: $σ_{xx}$ is $\sim e^2/h$ at $|E_F|<Δ$ and exponentially small otherwise. Two peaks of $σ_{xx}$ arising as $T\to 0$ are found to be strongly asymmetric.

cond-mat↗

arXiv1995

Weak levitation of 2D delocalized states in a magnetic field.

The deviation of the energy position of a delocalized state from the center of Landau level is studied in the framework of the Chalker-Coddington model. It is demonstrated that introducing a weak Landau level mixing results in a shift of the delocalized state up in energy. The mechanism of a levitation is a neighboring - Landau level - assisted resonant tunneling which ``shunts'' the saddle-points. The magnitude of levitation is shown to be independent of the Landau level number.

cond-mat↗