Vol 106, No 10 (2017)

The formation of amorphous structures in Si during the rapid quenching process was studied based on molecular dynamics simulation by using the Stillinger–Weber potential. The evolution characteristics of nanoclusters during the solidification were analyzed by several structural analysis methods. The amorphous Si has been formed with many tetrahedral clusters and few nanoclusters. During the solidification, tetrahedral polyhedrons affect the local structures by their different positions and connection modes. The main kinds of polyhedrons randomly linked with one another to form an amorphous network structures in the system. The structural evolution of crystal nanocluster demonstrates that the nanocluster has difficulty to growth because of the high cooling rate of 10¹² K/s.

Synchrotron X-ray diffraction studies of the structure of SnTe have been performed at room temperature and high pressures under the conditions of quasihydrostatic compression up to 193.5 GPa created in diamond anvil cells. Two structural phase transitions have been detected at P ≈ 3 and 23 GPa. The first phase transition is accompanied by a stepwise decrease in the volume of the unit cell by 4% because of the orthorhombic distortion of the initial SnTe-B1 cubic structure of the NaCl type. It has been found that two intermediate rhombic phases of SnTe with the space groups Cmcm and Pnma coexist in the pressure range of 3–23 GPa. The second phase transition at 23 GPa occurs from the intermediate rhombic modification to the SnTe-B2 cubic phase with the CsCl structure type. This phase transition is accompanied by an abrupt decrease in the volume of the unit cell by 8%. The pressure dependence of the volumes per formula unit at room temperature has been determined.

The possibility of creating dense ensembles of spin excitons, transferring them to macroscopic distances on the order of hundreds of microns, and recording the appearance of these excitons in the region spatially remote from the excitation point by means of simple techniques of photoexcitation and space-resolved detection of photoluminescence of a two-dimensional electron gas in a GaAs/AlGaAs quantum well has been demonstrated.

Two-dimensional turbulence has the striking tendency to self-organize into large-scale, coherent structures due to the inverse energy cascade. Here, we theoretically examine the case of a static pumping where the exciting force is independent of time; the case corresponds to the usual experimental setup. We establish dependence of the large-scale flow on the system parameters and the pumping characteristics for an unbound system and for a finite box.

Explicit expressions are found for the 6j symbols in symmetric representations of quantum su_N through appropriate hypergeometric Askey–Wilson (q-Racah) polynomials. This generalizes the well-known classical formulas for U_q(su²) and provides a link to conformal theories and matrix models.

The gravitational lensing of a finite star moving around a rotating Kerr black hole has been numerically simulated. Calculations for the direct image of the star and for the first and second light echoes have been performed for the star moving with an orbital period of 3.22 h around the supermassive black hole SgrA* at the center of the Galaxy. The time dependences for the observed position of the star on the celestial sphere, radiation flux from the star, frequency of detected radiation, and major and minor semiaxes of the lensed image of the star have been calculated and plotted. The detailed observation of such lensing requires a space interferometer such as the Russian Millimetron project.

A detailed study of the degree of circular polarization and the angular dependence of the emission spectra of an array of InAs quantum dots embedded in GaAs photonic nanostructures with chiral symmetry in the absence of an external magnetic field is carried out. A strong angular dependence of the spectra and the degree of circular polarization of radiation from quantum dots, as well as a significant effect of the lattice period of the photonic crystal on the radiation characteristics, is observed. The dispersion of photonic modes near the (±3, 0) and (±2, ±2) Bragg resonances is investigated in detail. The experimentally observed polarization, spectral, and angular characteristics of the quantum-dot emission are explained in the framework of a theory describing radiative processes in chiral photonic nanostructures.

The possibility of the dynamic compression of a polariton system in a planar microcavity after the end of a resonant pump pulse with the formation of the ground state of a condensate on the bottom of the polariton band has been studied. The studies of dynamics of a resonantly excited polariton gas in the mean field approximation have shown that such condensate state can be formed purely dynamically at excitation by coherent convergent Gaussian light pulses with a large aperture if the active region of the cavity is ahead of the waist of the Gaussian beam. The spatial distribution of polaritons in the formed high-density condensate has sharp edges and large jumps of the violet shift and quasimomentum on these edges prevent its monotonic expansion despite the repulsive interaction between polaritons. For this reason, the further evolution of the condensate is primarily due to the discharge of particles from its boundary and is accompanied by a decrease rather than an increase in the size of the high-density region at the initial stage. Thus, the self-sustained regime of the dynamic compression of the polariton condensate can be maintained for a relatively long time.