Electrical control of optical orientation of neutral and negatively charged excitons in n-type semiconductor quantum well

We report a giant electric field induced increase of spin orientation of excitons in n-type GaAs/AlGaAs quantum well. It correlates strongly with the formation of negatively charged excitons (trions) in the photoluminescence spectra. Under resonant excitation of neutral heavy-hole excitons, the polarization of excitons and trions increases dramatically with electrical injection of electrons within the narrow exciton-trion bias transition in the PL spectra, implying a polarization sensitivity of 200 % per Volt. This effect results from a very efficient trapping of neutral excitons by the quantum well interfacial fluctuations (so-called "natural" quantum dots) containing resident electrons.Comment: 18 pages, 4 figure

Spin-orbit terms in multi-subband electron systems: A bridge between bulk and two-dimensional Hamiltonians

We analyze the spin-orbit terms in multi-subband quasi-two-dimensional electron systems, and how they descend from the bulk Hamiltonian of the conduction band. Measurements of spin-orbit terms in one subband alone are shown to give incomplete information on the spin-orbit Hamiltonian of the system. They should be complemented by measurements of inter-subband spin-orbit matrix elements. Tuning electron energy levels with a quantizing magnetic field is proposed as an experimental approach to this problem.Comment: Typos noticed in the published version have been corrected and several references added. Published in the special issue of Semiconductors in memory of V.I. Pere

Spin-flip Raman scattering of the Γ\Gamma-X mixed exciton in indirect band-gap (In,Al)As/AlAs quantum dots

The band structure of type-I (In,Al)As/AlAs quantum dots with band gap energy exceeding 1.63 eV is indirect in momentum space, leading to long-lived exciton states with potential applications in quantum information. Optical access to these excitons is provided by mixing of the $\Gamma$- and X-conduction band valleys, from which control of their spin states can be gained. This access is used here for studying the exciton spin-level structure by resonant spin-flip Raman scattering, allowing us to accurately measure the anisotropic hole and isotropic electron $g$ factors. The spin-flip mechanisms for the indirect exciton and its constituents as well as the underlying optical selection rules are determined. The spin-flip intensity is a reliable measure of the strength of $\Gamma$-X-valley mixing, as evidenced by both experiment and theory.Comment: 5 pages, 3 figure

Retrospective Analysis of Enterovirus Infection Morbidity Rate in the Territory of the Amur Region and Peculiarities of Epidemic Process in the Period of Large-Scale Flood

There has been observed a tendency to increment of enterovirus morbidity rate over the past seven years. Foci of this infection have been formed in the area from time to time, with minor forms of the disease being predominant in clinical findings. Genetically enteroviruses circulating in the Amur Region have been characterized as homogenous; however there is a genetic relation among them with and, consequently, epidemiologic connection to enteroviruses originated from China. However, since May, 2013 there has been detected a boost activation of epidemic process as regards enteroviral infection, followed by the formation of two major foci with clustered infection, due to importation from Thailand as well. Emergency situation under conditions of flood (August-September, 2013) has contributed to aggravation of epidemiological situation on enteroviral infection. It has led to the increase in numbers of the exposed up to the maximum level for the past few years. In the territory of the temporal accommodation sites, where affected by high water and exposed to the infection population was placed, registered have been the cases of clustered enterovirus infection

First principles study of the origin and nature of ferromagnetism in (Ga,Mn)As

The properties of diluted Ga$_{1-x}$Mn$_x$As are calculated for a wide range of Mn concentrations within the local spin density approximation of density functional theory. M\"ulliken population analyses and orbital-resolved densities of states show that the configuration of Mn in GaAs is compatible with either 3d$^5$ or 3d$^6$, however the occupation is not integer due to the large $p$-$d$ hybridization between the Mn $d$ states and the valence band of GaAs. The spin splitting of the conduction band of GaAs has a mean field-like linear variation with the Mn concentration and indicates ferromagnetic coupling with the Mn ions. In contrast the valence band is antiferromagnetically coupled with the Mn impurities and the spin splitting is not linearly dependent on the Mn concentration. This suggests that the mean field approximation breaks down in the case of Mn-doped GaAs and corrections due to multiple scattering must be considered. We calculate these corrections within a simple free electron model and find good agreement with our {\it ab initio} results if a large exchange constant ($N\beta=-4.5$eV) is assumed.Comment: 15 pages, 14 figure

Epidemiological Features of Enterovirus Infection during Flood on the Territory of Jewish Autonomous Region

Long-term manifestations of epidemiological process of enterovirus infection in the Jewish Autonomous Region were similar to those in the Khabarovsk Territory, though with a lower intensity. After establishment of emergency situation regime, in view of the rainfall flooding in 2013, enterovirus morbidity rate had been increasing within three weeks duration, then started to fall rapidly. Clustered cases of enterovirus infection were not registered. Viral serous meningitis ratio was insignificant as minor forms of the disease prevailed; coxsackie virus A-9 and echovirus-6 dominated. During the flood period isolated from samples of patients with minor forms of enteroviral disease were three enterovirus strains, type 71, sub-genotype C4a, possessing a high degree of genetic similarity to the Chinese ones, 2010-2011. All in all impact of the natural disaster on the epidemiological situation on enteroviral infection in the Jewish Autonomous Region turned to be insignificant