arXiv subjects

O. Olendski

Publications and source records attributed to O. Olendski.

23 records · Page 2Linked to original sources

arXiv2014

Magnetic field control of the intraband optical absorption in two-dimensional quantum rings

Linear and nonlinear optical absorption coefficients of the two-dimensional semiconductor ring in the perpendicular magnetic field $\bf B$ are calculated within independent electron approximation. Characteristic feature of the energy spectrum are crossings of the levels with adjacent nonpositive magnetic quantum numbers as the intensity $B$ changes. It is shown that the absorption coefficient of the associated optical transition is drastically decreased at the fields corresponding to the crossing. Proposed model of the Volcano disc allows to get simple mathematical analytical results, which provide clear physical interpretation. An interplay between positive linear and intensity-dependent negative cubic absorption coefficients is discussed; in particular, critical light intensity at which additional resonances appear in the total absorption dependence on the light frequency, is calculated as a function of the magnetic field and levels' broadening.

cond-mat.mes-hall↗

arXiv2012

Influence of the interplay between de Gennes boundary conditions and cubicity of Ginzburg-Landau equation on the properties of superconducting films

Exact solutions of the Ginzburg-Landau (GL) equation for the straight film subjected at its edges to the Robin-type boundary conditions characterized by the extrapolation length $Λ$ are analyzed with the primary emphasis on the interaction between the coefficient $β$ of the cubic GL term and the de Gennes distance $Λ$ and its influence on the temperature $T$ of the strip. Very substantial role is played also by the carrier density $n_s$ that naturally emerges as an integration constant of the GL equation. Physical interpretation of the obtained results is based on the $n_s$-dependent effective potential $V_{eff}({\bf r})$ created by the nonlinear term and its influence on the lowest eigenvalue of the corresponding Schrödinger equation. In particular, for the large cubicities, the temperature $T$ becomes $Λ$ independent linearly decreasing function of the growing $β$ since in this limit the boundary conditions can not alter very strong $V_{eff}$. It is shown that the temperature increase, which is produced in the linear GL regime by the negative de Gennes distance, is wiped out by the growing cubicity. In this case, the decreasing $T$ passes through its bulk value $T_c$ at the unique density $n_s^{(0)}$ only, and the corresponding extrapolation length $Λ_{T=T_c}$ is an analytical function of $β$ whose properties are discussed in detail. For the densities smaller than $n_s^{(0)}$, the temperature stays above $T_c$ saturating for the large cubicities to the value determined by $n_s$ and negative $Λ$ while for $n_s>n_s^{(0)}$ the superconductivity is destroyed by the growing GL nonlinearity at some temperature $T>T_c$, which depends on $Λ$, $n_s$ and $β$. It is proved that the concentration $n_s^{(0)}$ transforms for the large cubicities into the density of the bulk sample.

cond-mat.mes-hall↗

arXiv2011

Guiding structures with multiply connected cross-sections: evolution of propagation in external fields at complex Robin parameters

Properties of the two-dimensional ring and three-dimensional infinitely long straight hollow waveguide with unit width and inner radius $ρ_0$ in the superposition of the longitudinal uniform magnetic field $\bf B$ and Aharonov-Bohm flux are analyzed within the framework of the scalar Helmholtz equation under the assumption that the Robin boundary conditions at the inner and outer confining walls contain extrapolation lengths $Λ_{in}$ and $Λ_{out}$, respectively, with nonzero imaginary parts. It is shown that, compared to the disk geometry, the annulus opens up additional possibilities of varying magnetization and currents by tuning imaginary components of the Robin parameters on each confining circumference; in particular, the possibility of restoring a lossless longitudinal flux by zeroing imaginary part $E_i$ of the total transverse energy $E$ is discussed. The energy $E$ turns real under special correlation between the imaginary parts of $Λ_{in}$ and $Λ_{out}$ with the opposite signs what physically corresponds to the equal transverse fluxes through the inner and outer interfaces of the annulus. In the asymptotic case of the very large radius, simple expressions are derived and applied to the analysis of the dependence of the real energy $E$ on $Λ_{in}$ and $Λ_{out}$. New features also emerge in the magnetic field influence; for example, if, for the quantum disk, the imaginary energy $E_i$ is quenched by the strong intensities $B$, then for the annulus this takes place only when the inner Robin distance $Λ_{in}$ is real; otherwise, it almost quadratically depends on $B$ with the corresponding enhancement of the reactive scattering. Closely related problem of the hole in the otherwise uniform medium is also addressed for real and complex extrapolation lengths with the emphasis on the comparative analysis with its dot counterpart.

cond-mat.mes-hall↗

arXiv2008

Two-dimensional magnetoexcitons in the presence of spin-orbit coupling

We study theoretically the effect of spin-orbit coupling on quantum well excitons in a strong magnetic field. We show that, in the presence of an in-plane field component, the excitonic absorption spectrum develops a double-peak structure due to hybridization of bright and dark magnetoexcitons. If the Rashba and Dresselhaus spin-orbit constants are comparable, the magnitude of splitting can be tuned in a wide interval by varying the azimuthal angle of the in-plane field. We also show that the interplay between spin-orbit and Coulomb interactions leads to an anisotropy of exciton energy dispersion in the momentum plane. The results suggest a way for direct optical measurements of spin-orbit parameters.

cond-mat.mes-hall↗

arXiv2007

Anisotropic spin relaxation in quantum dots

We study theoretically phonon-assisted spin relaxation of an electron confined in an elliptical quantum dot (QD) subjected to a tilted magnetic field. In the presence of both Rashba and Dresselhaus spin-orbit terms, the relaxation rate is anisotropic with respect to the in-plane field orientation. This anisotropy originates from the interference, at nonzero tilt angle, between the two spin-orbit terms. We show that, in a narrow range of magnetic field orientations, the relaxation rate exhibits anomalous sensitivity to variations of the QD parameters. In this range, the relative change in the relaxation rate with in-plane field orientation is determined {\em solely} by the spin-orbit coupling strengths and by the dot geometry. This allows simultaneous determination of both Rashba and Dresselhaus coupling parameters and the dot ellipticity from analysis of the angular dependence of the relaxation rate.

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