arXiv subjects

F. T. Vasko

Publications and source records attributed to F. T. Vasko.

42 records · Page 3Linked to original sources

arXiv2003

Spin-dependent Rabi oscillations in single quantum=0D dot

Ultrafast optical pump of exciton resonance in single quantum dot by an elliptically polarized laser pulse is described by the non-Markov balance equations. Population and spin dynamics are investigated and spin-dependent Rabi oscillations are considered for the case of a flat quantum dot, with the lateral size greater than the height. The following peculiarities of temporal evolution have been found: a) a beating of Rabi oscillations under an elliptically polarized pump and b) quenching of spin orientation due to a spin-orbit splitting effect.

cond-mat.mtrl-sci↗

arXiv2003

Rabi oscillations of 2D electrons under ultrafast intersubband excitation

We investigate coherent nonlinear dynamics of 2D electrons under ultrafast intersubband excitation by mid-IR pulses. We include the effects of relaxation and dephasing, both homogeneous and inhomogeneous, as well as detuning within a non-Markovian equation to obtain temporal population redistributions. We show how, using a cross-correlation method, the effects of Rabi oscillations may be detected in this system, and briefly discuss other detection methods.

cond-mat.stat-mech↗

arXiv2002

KP-approach for non-symmetric short-range defects: resonant states and alloy bandstructure

The short-range defect with reduced symmetry is studied in the framework of KP-approach taking into account a matrix structure of potential energy in the equations for envelope functions. The case of the narrow-gap semiconductor, with defects which are non-symmetric along the [001], [110], or [111] directions, is considered. Resonant state at a single defect is analyzed within the Koster-Slater approximation. The bandstructure modification of the alloy, formed by non-symmetric impurities, is discussed and a generalized virtual crystal approximation is introduced.

cond-mat.mtrl-sci↗

arXiv2000

Inhomogeneous broadening of tunneling conductance in double quantum wells

The lineshape of the tunneling conductance in double quantum wells with a large-scale roughness of heterointerfaces is investigated. Large-scale variations of coupled energy levels and scattering due to the short-range potential are taken into account. The interplay between the inhomogeneous broadening, induced by the non-screened part of large-scale potential, and the homogeneous broadening due to the scattering by short-range potentials is considered. It is shown that the large inhomogeneous broadening can be strongly modified by nonlocal effects involved in the proposed mechanism of inhomogeneity. Related change of lineshape of the resonant tunneling conductance between Gaussian and Lorentzian peaks is described. The theoretical results agree quite well with experimental data.

cond-mat.mes-hall↗

arXiv2000

Two-subband electron transport in nonideal quantum wells

Electron transport in nonideal quantum wells (QW) with large-scale variations of energy levels is studied when two subbands are occupied. Although the mean fluctuations of these two levels are screened by the in-plane redistribution of electrons, the energies of both levels remain nonuniform over the plane. The effect of random inhomogeneities on the classical transport is studied within the framework of a local response approach for weak disorder. Both short-range and small-angle scattering mechanisms are considered. Magnetotransport characteristics and the modulation of the effective conductivity by transverse voltage are evaluated for different kinds of confinement potentials (hard wall QW, parabolic QW, and stepped QW).

cond-mat.mes-hall↗

arXiv1999

Energy spectrum, density of states and optical transitions in strongly biased narrow-gap quantum wells

We study theoretically the effect of an electric field on the electron states and far-infrared optical properties in narrow-gap lead salt quantum wells. The electron states are described by a two-band Hamiltonian. An application of a strong electric field across the well allows the control of the energy gap between the two-dimensional (2D) states in a wide range. A sufficiently strong electric field transforms the narrow-gap quantum well to a nearly gapless 2D system, whose electron energy spectrum is described by linear dispersion relations ε_σ (k) ~\pm (k-k_σ), where k_σ are the field-dependent 2D momenta corresponding to the minimum energy gaps for the states with spin numbers σ. Due to the field-induced shift of the 2D subband extrema away from k=0 the density of states has inverse-square-root divergencies at the edges. This property may result in a considerable increase of the magnitude of the optical absorption and in the efficiency of the electrooptical effect.

cond-mat.mes-hall↗