V. M. Kovalev

Magnetoexcitons in type-II quantum dots

The ground state of a spatially indirect exciton in type-II quantum dots with a short-range potential acquires nonzero angular momentum in the presence of a magnetic field oriented perpendicular to the plane of the system. The critical magnetic field of the transition to a ground state with nonzero angular momentum depends on the radius of the quantum dot. Such a transition can be observed as quenching of luminescence by a magnetic field in quantum dots of the GaSb/GaAs system, for example.

Solitons in semiconductor microstructures with a two-dimensional electron gas

Nonlinear waves in a two-dimensional electronic plasma with metal screening gates are investigated. It is shown that solitons described by the KdV equation exist in such a system.

Modulation of the exciton density in a hybrid electron-exciton system

The induced modulation of the exciton density in a system consisting of spatially separated layers of a two-dimensional electron gas and indirect dipolar excitons is studied theoretically. In particular, it is shown that an external potential causes Friedel oscillations in the density of excitons due to their interaction with electrons. Possibilities for experimental observation of this effect are briefly discussed.

Screening of Static Perturbation in a System of Dipole Excitons

The screening of local electrostatic perturbation by indirect excitons has been investigated. It has been shown that the linear screening is dielectric, and the effective dielectric constant may be large in the case of high degeneracy of the Bose gas of excitons. The emergence of a condensate significantly changes the behavior of the perturbation potential at infinity, leading to power-law asymptotic behavior with large exponents. In the nonlinear regime, the screened potential is saturated with an unlimited increase in the initial perturbation.

Effect of exciton dragging by a surface acoustic wave

We present the theory of the effect of exciton dragging by a Rayleigh surface acoustic wave at temperatures above the condensation temperature of the exciton gas and at zero temperature, where the effects of the Bose-Einstein condensation of the exciton gas are most pronounced. The magnitude of the acoustic drag flux in the exciton gas at high temperatures has been calculated taking into account the exciton-exciton interaction. It has been shown that the drag flux at typical experimental parameters (at a given intensity of the surface acoustic wave (SAW)) is independent of the frequency of the acoustic wave, whereas the interaction between excitons leads to screening of the SAW-induced perturbation, which results in an exponentially fast decrease in the drag flux with an increase in the exciton density. At low temperatures, in the presence of a condensate, the drag flux of condensate particles exhibits a resonance character when the velocity of Bogoliubov excitations approaches the velocity of the acoustic wave and the magnitude of the flux is linear in the SAW frequency. The drag flux of the above-condensate particles has a threshold character: the above-condensate particles are dragged by the wave at a velocity of the acoustic wave higher than the bogolon velocity. The magnitude of the above-condensate flux is inversely proportional to the SAW frequency.

Absorption of surface acoustic waves by a gas of two-dimensional indirect excitons

Absorption of a Bleustein-Gulyaev surface acoustic wave interacting with a gas of two-dimensional indirect excitons has been calculated. It has been shown that the absorption is changed considerably when the excitons undergo Bose-Einstein condensation. This can serve as experimental evidence of such a transition.

Response of a Bose-Einstein condensate of dipole excitons to static and dynamic perturbations

Studies of the interaction of a Bose-Einstein condensate of two-dimensional spatially indirect excitons with the static fields of impurities, surface acoustic waves, and elementary excitations of a degenerate electron gas have been reviewed. The effects of screening of charged impurities and absorption of a Bleustein-Gulyaev surface acoustic wave by an exciton condensate have been considered. Friedel oscillations of the exciton density in a hybrid electron-exciton system, which consists of spatially separated layers of condensed exciton gas and degenerate electron gas, have been studied. The lifetimes of quasiparticle excitations (electrons, plasmons, and bogolons) in the hybrid system have been calculated. The contributions to the effects under study from condensate and above-condensate particles have been determined. The properties of an excitonic insulator have been analyzed within the Bardeen-Cooper-Schrieffer model with a built-in dissipation-free current.

Lifetime of quasiparticles in a hybrid electron-exciton system

The lifetimes (damping) of one-body and collective excitations in a hybrid system consisting of spatially separated layers of a two-dimensional electron gas and a gas of indirect excitons have been calculated at zero temperature in the presence of the Bose-Einstein condensate of excitons. It has been shown that the electron-exciton interaction leads to a considerable shortening of the lifetime of electrons as compared to the electron-electron interaction and to the appearance of a nonzero (linear in the wave vector) damping of plasmons. The interaction of the exciton Bose gas with the electron layer induces damping of Bogoliubov phonons in the exciton Bose gas, which is, however, much lower than their intrinsic (Belyaev) damping.

Aharonov-Bohm effect for plasmons in a finite-width quantum ring

The magnetoplasma oscillation frequencies of the 2D electrons in a quantum ring have been found taking into account the finite width of the ring in the model allowing for an exact solution for the single-particle spectrum. It is shown that instead of the periodic oscillations of the plasmon frequency ω typical of the 1D ring, ω in the case under consideration depends on the magnetic flux with the frequency and amplitude modulations: the period of oscillations as a function of the magnetic flux and their amplitude depend on the magnetic field strength.

Composite particles in quantum wells

Bound states of composite particles in single and double quantum wells are studied. The spectrum and polarizability of an indirect trion and an indirect D− center (a negatively charged donor) in crossed electric and magnetic fields are found. Bound dielectron states in a single quantum well are studied. The possibility of observing a dielectron experimentally by the magnetic-dipole absorption of electromagnetic waves is pointed out.