Vol 106, No 11 (2017)

The crystal structure of elemental Sn was investigated by synchrotron X-ray diffraction at ultra high pressures up to ∼230 GPa creating in diamond anvil cells. Above 70 GPa, a pure bcc structure of Sn was observed, which is stable up to 160GPa, until an occurrence of the hcp phase was revealed. At the onset of the bcc-hcp transition at pressure of about 160GPa, the drop of the unit cell volume is about 1%. A mixture of the bcc-hcp states was observed at least up to 230GPa, and it seems that this state could exist even up to higher pressures. The fractions of the bcc and hcp phases were evaluated in the pressure range of the phase coexistence 160–230 GPa. The difference between static and dynamic compression and its effect on the V–P phase diagram of Sn are discussed.

Electron paramagnetic resonance (EPR) and magnetostriction of the Cu₂MnBO₅ single crystal have been studied. The EPR spectrum consists of a single Lorentzian line due to the exchange-coupled system of spins of Cu²⁺ and Mn³⁺ ions. It has been established experimentally that the g-factor in the paramagnetic region is strongly anisotropic and anomalously small, which is not typical of the exchange-coupled system of spins of Cu²⁺ and Mn³⁺ ions. At a temperature of 150 K, the g-factors along the crystallographic a, b, and c axes are 2.04, 1.96, and 1.87, respectively. Such small effective g-factor values can be due to the effect of the anisotropic Dzyaloshinskii–Moriya exchange interaction between the spins of Cu²⁺ and Mn³⁺ ions directed along the a axis. The presence of two Cu²⁺ and Mn³⁺ Jahn–Teller ions occupying four nonequivalent positions in the crystal is responsible for the absence of the inversion center. It is found that the behavior of the magnetostriction of Cu₂MnBO₅ is not typical of transition-metal crystals but is closer to the behavior of crystals containing rare-earth ions.

Cyclotron resonance spectra in high magnetic fields up to 34 T in InAs/GaSb/InAs “three-layer” quantum wells with gapless Dirac fermions have been studied. In quantizing magnetic fields, an absorption line associated with transitions from the lower Landau levels of electrons in a subband with a “conical” dispersion relation has been detected. Experimental energies of the transitions have been compared to theoretical calculations with the eight-band Kane Hamiltonian. The results confirm the gapless band structure of the studied samples.

Experimental results indicating a direct disorder-induced superconductor–insulator transition in NbTiN thin films have been reported. It has been shown that an increase in the resistance per square in the normal state is accompanied by the suppression of the critical temperature of the superconducting transition T_c according to the fermion mechanism of suppression of superconductivity by disorder. At the same time, the temperature of the Berezinskii–Kosterlitz–Thouless transition is completely suppressed at a nonzero critical temperature and, then, the ground state changes to insulating, which is characteristic of the boson model of suppression of superconductivity by disorder. It has been shown that the temperature dependences of the resistance of insulating films follow the Arrhenius activation law.

Observation of a narrow structure at W ∼ 1.68 GeV in the excitation functions of some photon- and pion-induced reactions may signal a new narrow isospin-1/2 N(1685) resonance. New data on the _γN → πηN reactions from GRAAL seems to reveal the signals of both N⁺(1685) and N⁰(1685) resonances.

We report the first experimental observation of backward terahertz emission from the two-color laser induced plasma filament in air. The ratio of measured forward-to-backward terahertz radiation is ∼25/1. This result agrees with numerical simulations based on interferometric model assuming 0.3 mm long plasma source.

A dielectric metasurface at the variation of the refractive index of the environment has been numerically simulated. The optical response of the metasurface contacting both a homogeneous medium with different refractive indices and a liquid crystal controlled by the temperature and applied electric field has been considered. The results can be used to produce optical devices for various aims. Numerical simulations have been performed for the parameters of the liquid crystal E7 widely used in industry.

Vortex solutions of coupled Gross–Pitaevskii equations for a two-component Bose–Einstein condensate of exciton polaritons have been described theoretically with the inclusion of the dependence of the Rabi splitting energy on the density of the exciton component. It has been shown that the inclusion of blueshift leads to a considerable decrease in the densities of both components of the condensate. The spatial profiles of excitons and photons in the polariton system, as well as the energy of vortex excitation formation, have been calculated taking into account nonlinear corrections.

The previously developed model of an intermediate phase of ice with a liquid system of hydrogen bonds has been applied to describe a quasiliquid surface layer. This approach leads to a two-component model of a quasiliquid ice surface layer. In the outer part of the layer, both the proton and oxygen sublattices are melted, constituting water or the Thomson sublayer. In the inner part of the layer, only the proton sublattice is melted, whereas the oxygen sublattice holds its structure (the liquid state of the system of hydrogen bonds or the Faraday sublayer). The proposed model gives correct-in-magnitude estimates of various physical characteristics of the layer, explains the contradiction between the Faraday and Thomson hypotheses, and is consistent with recent experimental results and numerical studies.