Optical orientation of the homogeneous non-equilibrium Bose-Einstein condensate of bright excitons (polaritons)

A simple model, describing the dynamics of the non-equilibrium pseudospin of a homogeneous Bose-Einstein condensate of exciton polaritons, has been formulated. It explains the suppression of spin splitting of a non-equilibrium polariton condensate in an external magnetic field, the optical alignment, and the conversion of alignment into orientation of polaritons. It has been shown that inverse effects are possible, to wit, the spontaneous circular polarization and the enhancement of spin splitting of a non-equilibrium condensate of polaritons in the absence of external field.Comment: 21 pages, 2 figure

Nuclear spin warm-up in bulk n-GaAs

We show that the spin-lattice relaxation in n-type insulating GaAs is dramatically accelerated at low magnetic fields. The origin of this effect, that cannot be explained in terms of well-known diffusion-limited hyperfine relaxation, is found in the quadrupole relaxation, induced by fluctuating donor charges. Therefore, quadrupole relaxation, that governs low field nuclear spin relaxation in semiconductor quantum dots, but was so far supposed to be harmless to bulk nuclei spins in the absence of optical pumping can be studied and harnessed in much simpler model environment of n-GaAs bulk crystal.Comment: 5 pages, 4 figure

Longitudinal and transversal spin dynamics of donor-bound electrons in fluorine-doped ZnSe: spin inertia versus Hanle effect

The spin dynamics of the strongly localized, donor-bound electrons in fluorine-doped ZnSe epilayers is studied by pump-probe Kerr rotation techniques. A method exploiting the spin inertia is developed and used to measure the longitudinal spin relaxation time, $T_1$, in a wide range of magnetic fields, temperatures, and pump densities. The $T_1$ time of the donor-bound electron spin of about 1.6 $\mu$s remains nearly constant for external magnetic fields varied from zero up to 2.5 T (Faraday geometry) and in a temperature range $1.8-45$ K. The inhomogeneous spin dephasing time, $T_2^*=8-33$ ns, is measured using the resonant spin amplification and Hanle effects under pulsed and steady-state pumping, respectively. These findings impose severe restrictions on possible spin relaxation mechanisms.Comment: 10 pages, 7 figure

Fine structure and optical pumping of spins in individual semiconductor quantum dots

We review spin properties of semiconductor quantum dots and their effect on optical spectra. Photoluminescence and other types of spectroscopy are used to probe neutral and charged excitons in individual quantum dots with high spectral and spatial resolution. Spectral fine structure and polarization reveal how quantum dot spins interact with each other and with their environment. By taking advantage of the selectivity of optical selection rules and spin relaxation, optical spin pumping of the ground state electron and nuclear spins is achieved. Through such mechanisms, light can be used to process spins for use as a carrier of information

Особенности разработки контактной системы СВЧ-переключателя диапазона частот до 18 ГГц

The paper describes the development results and the construction of the high frequency contact system of the electromechanical microwave switch with the frequency range up to 18 GHz. The S-parameter measurement suggests that the achieved results are in line with the best in class competitive devices.The construction features the radially cut support beads, which enable simple and low-cost coaxial connector design that takes advantage of the monolithic center conductor design. The effects of the size of the radial cut on the effective dielectric parameters are researched using the quarter wavelength resonator method. The presented results of the research allow the accounting of the cut size on the microwave parameters of the switch. The presented construction of the developed resonator allows the coaxial support bead dielectric parameters control, implemented in the manufacturing process of the switch. Korenev A. V. Special Considerations of the Development of the Contact System of the Microwave Switch with the Frequency Range up to 18 GHz. Ural Radio Engineering Journal. 2023;7(1):23–36. (In Russ.) DOI 10.15826/ urej.2023.7.1.002.В статье приведены результаты разработки и конструкция высокочастотной контактной системы электромеханического СВЧ-переключателя, работающего в диапазоне частот до 18 ГГц. Результаты измерения S-параметров разработанной контактной системы свидетельствуют о достигнутых характеристиках, соответствующих лучшим мировым аналогам. Описан опыт применения опорных шайб с разрезом, которые позволяют упростить конструкцию соединителей СВЧ-переключателя и снизить их себестоимость. Исследована зависимость эффективной диэлектрической проницаемости шайб от величины угла и формы разреза. Для контроля диэлектрических параметров шайб был использован метод четвертьволнового коаксиального резонатора. Приведена конструкция резонатора и результаты измерения параметров шайб.Метод четвертьволнового резонатора использован в производственном процессе для контроля параметров шайб и их отбраковки на ранних стадиях технологического цикла. Коренев А. В. Особенности разработки контактной системы СВЧ-переключателя диапазона частот до 18 ГГц. Ural Radio Engineering Journal. 2023;7(1):23–36. DOI 10.15826/urej.2023.7.1.002