Vol 108, No 3 (2018)

self-consistent approach to anharmonic effects based on the quantum many-body theory is for the first time used to calculate the quadrupole moments of the lowest 3^– states in Sn and Pb isotopes, including the ¹⁰⁰Sn, ¹³²Sn, and ²⁰⁸Pb doubly magic ones. The consistency between the mean nuclear field and the effective interaction is maintained using the energy-density-functional method with known parameters of the Fayans functional. Thereby, the quadrupole moments of the lowest 3^– states of isotopes with nucleon pairing are reliably predicted, and the existing data for the ²⁰⁸Pb isotope are reproduced. It has been shown that the new three-quasiparticle correlations are responsible for slightly more than half of the observed effect and the remaining part is due to the quadrupole polarizability of the nucleus.

The Compton scattering of attosecond X-ray pulses on a hydrogen atom has been studied theoretically in terms of the spectral angular scattering probability during the action of a pulse. The dependence of scattering on the carrier frequency, pulse duration, and scattering angle has been analyzed. It has been shown that the probability of the process at certain parameters of the problem is a nonlinear function of the pulse duration.

A model of two media with Kerr defocusing nonlinearity separated by a planar interface interacting nonlinearly with excitations has been considered. Two new types of stationary states describing the transformation of a soliton lattice to a damping field at the passage through such an interface have been found. These two types of states differ in the energy range of existence and in the character of field damping with the distance from the interface. The energies of long-wavelength states have been obtained. The conditions of the existence of such states have been determined depending on the characteristics of media and the interface between them.

The density functional theory is used to calculate the energy of an electron–hole liquid in Si/Si_1–xGe_x/Si quantum wells. Three one-dimensional nonlinear Schrödinger equations for electrons and light and heavy holes are solved numerically. It is shown that, in shallow quantum wells (small x), both light and heavy holes exist in the electron–hole liquid. Upon an increase in the Ge content, a transition to a state with one type of holes occurs, with the equilibrium density of electron–hole pairs decreasing by more than a factor of 2.

A system of equations describing the ground state in an external magnetic field has been obtained for a twoposition antiferromagnet with noncollinear axes of single-ion anisotropy of moments of different sublattices. It has been shown that the antiferromagnetism vector changes sign at a spin-flop transition. This leads to a first-order magnetic phase transition with hysteresis in the field dependence of the magnetization. Explicit relations have been obtained between the parameters of a microscopic Hamiltonian and the experimentally observed spontaneous moment and spin-flop transition field. It has been shown that the field dependence of the total magnetic moment of the antiferromagnet with magnetic ions at two crystallographically nonequivalent positions (two-position antiferromagnet) obtained within the two-sublattice model is nonlinear above the transition field at any orientation of the crystal with respect to the magnetic field.

Spin-dependent electronic transport is theoretically investigated for double-barrier hybrid structures S–IF–F–IF–N and S–IF–N–IF–N, where S is a superconductor; F and N are ferromagnetic and normal metals, respectively; and IF is the spin-active barrier. It is shown that in the case of strong superconducting proximity effect and sufficiently thin F layers, the differential resistance of such structures can become negative at some voltages, and the voltage dependence of the current can have an N-shaped form. Characteristic feature of the differential resistance is its asymmetric dependence on voltage, which is most clearly manifested at strong polarization of at least one of the barriers. The influence of impurity spin–orbit scattering processes in the N-layer located between the barriers is investigated. The study was carried out for the case of diffusion electron transport.

The temperature dependence of the microwave photovoltage has been studied in microwave-induced states of a two-dimensional electron system, which are characterized by an almost dissipationless flow of a low-frequency current. At decreasing temperature, a smooth transition has been found from a bistable state, where the photovoltage demonstrates switching between two levels, which are due to reversals of the spontaneous electric field in a domain structure, to a steady state. The transition occurs as the shift of one of the levels of the bistable photovoltage to the other level accompanied by a decrease in the switching frequency. The results indicate the freezing of the dynamic domain structure in the state corresponding to the more stable configuration of the electric field.