High spin polarization of optically-oriented trions in p-doped GaAs-AlGaAs quantum wells

We performed cw-photoluminescence (PL) measurements on a 15 nm wide p-doped Al0.3Ga0.7As-GaAs-Al0.3Ga0.7As quantum well structure at low temperatures. By irradiating the sample with circularly polarized light and analyzing the degree of circular polarization of the PL signal, we found a significantly higher degree of spin polarization for charged excitons (trions) than for neutral excitons. Time-resolved pump-probe and Faraday-rotation experiments give an additional information concerning the exciton and trion resonant photoexcitation

Nonlinear magneto-gyrotropic photogalvanic effect

We report on the observation of magnetic-field-induced photocurrent in HgTe/HgCdTe quantum wells of different widths. Both the intrasubband and interband absorption of infrared/terahertz radiation in the heterostructures is shown to cause a dc electric current in the presence of an in-plane magnetic field. The photocurrent behavior upon variation in the radiation polarization, magnetic-field strength, and temperature is studied. At a moderate magnetic field the current exhibits a linear field dependence. At high magnetic fields, however, it becomes nonlinear and is dominated by a cubic in magnetic-field contribution. The latter effect is observed in quantum wells with the inverted band structure only. The experimental results are analyzed in terms of the phenomenological theory and microscopic models of magnetogyrotropic photogalvanic effect based on asymmetry of optical transitions and/or asymmetric relaxation of carriers in the momentum space. The effect is shown to be related to the gyrotropic properties of the structures. The developed theory of magnetogyrotropic photocurrent describes well all experimental results. It is shown that both intrasubband and interband optical transitions may lead to spin-related as well as to spin-independent magnetic-field-induced photocurrents

Bulk plasmon-phonon polaritons in n-GaN

We studied theoretically and experimentally plasmon-phonon polaritons and longitudinal plasmon-phonon oscillations in n-GaN epitaxial layers. The studies were carried out on the epitaxial layers with various doping levels. Simulation of the reflectivity spectra and dispersion relations of plasmon-phonon polaritons was performed in a wide frequency range. Reflectivity spectra transformation associated with phonon damping and electron relaxation processes has been revealed. Experimental studies of the reflectivity spectra have been performed in the spectral range of 8-80 meV. The experimental spectra are well fitted by the simulated ones. Results of the study can be used for contactless determination of the electron concentration and mobility in GaN epitaxal layers.Peer reviewe

Development of a Numerical Method for Calculating a Gas Supply System during a Period of Change in Thermal Loads

Nowadays, modern gas supply systems are complex. They consist of gas distribution stations; high-, medium-, and low-pressure gas networks; gas installations; and control points. These systems are designed to provide natural gas to the population, including domestic, industrial, and agricultural consumers. This study is aimed at developing methods for improving the calculation of gas distribution networks. The gas supply system should ensure an uninterrupted and safe gas supply to consumers that is easy to operate and provides the possibility of shutting down its individual elements for preventive, repair, and emergency recovery work. Therefore, this study presents a mathematical calculation method to find the optimal operating conditions for any gas network during the period of seasonal changes in thermal loads. This method demonstrates how the reliability of gas distribution systems and resistance to non-standard critical loads are affected by consumers based on the time of year, month, and day, and external factors such as outdoor temperature. The results in this study show that this method will enable the implementation of tools for testing various management strategies for the gas distribution network

Excitation and decay of surface plasmon polaritons in n-GaN

We report on the studies of the surface plasmon polaritons in n-GaN epitaxial layers. The grating etched on the surface of the epitaxial layer is used to excite surface plasmon polaritons by means of terahertz photons. The experimental reflectivity spectrum for p-polarized radiation demonstrates a set of resonances associated with excitation of different surface plasmon polariton modes. Spectral peculiarities due to the diffraction effect have been also revealed. Emission of terahertz radiation is investigated under epilayer temperature modulation by electric current. The emissivity spectrum of the epitaxial layer with surface-relief grating shows peaks in the frequency ranges corresponding to the decay of the surface plasmon polariton modes. The characteristic features of the reflectivity and emissivity spectra are well described theoretically by a differential method with explicit integration scheme.Peer reviewe