A. V. Shorokhov

Hybrid–impurity resonances in anisotropic quantum dots

The absorption of electromagnetic radiation of an anisotropic quantum dot is theoretically investigated taking into account the processes associated with simultaneous scattering from ionized impurities. It is shown that the scattering of electrons by impurities leads to the resonance absorption even if we have only one impurity in the quantum dot. Explicit formula is derived for the absorption coefficient. The positions of the resonances peaks are found. The effects of external magnetic field on the resonance absorption are studied.

Physical principles of the amplification of electromagnetic radiation due to negative electron masses in a semiconductor superlattice

In a superlattice placed in crossed static electric and magnetic fields, under certain conditions, the inversion of electron population can appear at which the average energy of electrons is above the middle of the mini-band and the effective mass of the electron is negative. This is the implementation of the negative effective mass amplifier and generator (NEMAG) in the superlattice. It can result in the amplification and generation of terahertz radiation even in the absence of negative differential conductivity.

High-frequency absorption and gain in superlattices: Semiquasistatic approach

We consider a generation and an amplification of THz radiation in semiconductor superlattices under the action of microwave pump field. Electrons belonging to a single miniband of the superlattice interact quasistatically with the pump field and dynamically with a signal THz field. Within this semiquasistatic approach we derive elegant difference formulas describing absorption (gain) of the weak THz signal. We present an instructive geometric interpretation of the absorption formulas which allows a search of optimum conditions for the gain employing only a simple qualitative analysis. Our theoretical findings contribute to the development of sources and detectors of THz radiation that are using nonlinear electric properties of semiconductor superlattices.

Generation of direct current in a semiconductor superlattice under the action of a bichromatic field as a parametric effect

Generation of direct current in a semiconductor superlattice under the action of an ac bichromatic field is considered in the most general case of an arbitrary ratio of the frequencies of the fields being mixed. It is shown that this effect is of parametric origin associated with oscillations of the electron effective mass in the miniband of the superlattice.

Terahertz parametric gain in semiconductor superlattices

We consider a high-frequency response of electrons in a single miniband of superlattice subject to dc and ac electric fields. Action of ac electric field causes oscillations of electrons effective mass in miniband, which result in a parametric resonance. We have established a theoretical feasibility of phase-sensitive parametric amplification at the resonance. The parametric amplification does not require operation in conditions of negative differential conductance. Therefore a formation of destructive domains of high electric field inside the superlattice can be prevented. Here we concentrate on the parametric up- and down-conversion of electromagnetic radiation from available frequencies to desirable THz frequency range.

Magnetic response of an electron gas in a quantum ring of non-zero width

Abstract An investigation of the magnetic moment of an electron gas in a quantum ring of non-zero width is made. Analytic expressions are obtained for the magnetic moment. For the magnetic moment of the system, the dependence on temperature and parameters of the ring are found and investigated in detail. De Haas–van Alphen and Aharonov–Bohm oscillations are investigated.

THEORETICAL BACKGROUNDS OF NONLINEAR THz SPECTROSCOPY OF SEMICONDUCTOR SUPERLATTICES

We consider terahertz absorption and gain in a single miniband of semiconductor superlattice subject to a bichromatic electric field in the most general case of commensurate frequencies of the probe and pump fields. Using an exact solution of Boltzmann transport equation, we show that in the small-signal limit the formulas for absorption always contain two distinct terms related to the parametric and incoherent interactions of miniband electrons with the alternating pump field. It provides a theoretical background for a control of THz gain without switching to the negative differential conductivity state. For pedagogical reasons we present derivations of formulas in detail.

Quantum derivatives and terahertz gain in a superlattice

Simple formulas describing terahertz absorption and gain in a semiconductor superlattice irradiated by a microwave pump field are derived for the case when the signal frequency is a half harmonic of the pump. A simple qualitative analysis provides a geometric interpretation of the derived formulas, which can be used to determine if gain is feasible.

Quantization of Acoustoelectric Current in a Ballistic Channel

The electric current induced by an ultrasonic phonon flux in a ballistic quasi-two-dimensional quantum channel is investigated theoretically. Two types of confining potential are considered. An analytic expression for the acoustoelectric current is derived, and its dependence on the chemical potential and on the magnitude of the longitudinal magnetic field is investigated. It is shown that the dependence of the acoustoelectric current on the chemical potential may be of the experimentally observed step type. The oscillatory dependence of the acoustoelectric current on the magnetic field is considered for the cases of weak and strong magnetic quantization.

Generation of high-frequency radiation and instability of space-charge waves in semiconductor superlattices

We investigated the instability of space-charge waves in SSL in the conditions of the schemes of generation based on the the generalized LSA scheme. We demonstrate that in general case the condition for space-charge instability depends on the wave vector of perturbation k. This effect can change conditions for the operation in generalized limited space-charge accumulation mode of Bloch oscillator.