The one-dimensional Kane oscillator in a thermal bath is studied. It is found that the heat capacity of Kane electrons is four times greater than the heat capacity of the one-dimensional harmonic oscillator for higher temperatures.

In this work, Rb2SO4 single crystals of good optical quality were synthesized and the spectral (300–700 nm) and temperature (300–77 K) dependencies of birefringence were experimentally investigated. It was found that with a temperature decreasing, at a temperature of T = 85 K and a light wavelength of λ = 500 nm, the birefringence value in the Y direction is zero (Δny = nz – nх = 0), which testifies to the existence of a new isotropic point. The influence of uniaxial compression on changes in Δny (Т, λ) was studied, and their significant sensitivity was revealed. The temperature-baric and spectral-baric changes of the isotropic point position were analyzed, based on which the temperature-spectral-baric diagram of the isotropic state of the crystal was constructed, which will be of practical importance for the use of crystal as an active element in a crystal-optical temperature sensor for a low-temperature region. Based on the Δny (Т, λ, σ) dependencies, the combined piezo-optic coefficients of the crystal were estimated, and it was assumed that not only thermal but also mechanical deformation of the optical indicatrix takes place in the vicinity of the isotropic point.

We study the transport properties of a two-dimensional electron system with an essential spin-orbit interaction under topological phase transition due to changing in-plane magnetic field. We have analyzed the contribution of diagonal and off-diagonal components of density matrix with respect to number of spin zone in the high-frequency conductivity. Analytical formulas for the conductivity tensor have been obtained. A numerical analysis giving full enough representation about the dependence of the conductivity on frequency and magnetic field is presented. We have shown that the contribution of the off-diagonal elements of density matrix is the greater than the higher the frequency of the alternating electromagnetic field. It has been established that for magnetic field value at which the minimum electron energy of upper spin zone exceeds the Fermi energy, the conductivity as a function of magnetic field change in discrete step.

The collective oscillations of systems of Xe atoms adsorbed in a groove between two carbon nanotubes have been studied by the method of molecular dynamics. The one-dimensional and three-chain structures of atoms that appear in such grooves are considered depending on the number of particles, temperature, and external potentials. It is shown that the infinite one-dimensional structures of Xe atoms are stable at finite temperatures only in the presence of such potentials acting in the direction normal to the axis of the structure. The oscillation spectrum is found, which is in accordance with theoretical calculations of the dispersion laws of collective modes. Collective oscillations of three-chain structures have been studied. The theoretical calculation of the laws of dispersion of modes, carried out by the method of equations of motion for small displacements of atoms from the equilibrium position, showed that the collective modes of the system show a great similarity with the corresponding dispersion laws of a one-dimensional chain of atoms. At the same time, it was found that a torsion mode arises, which is characteristic of a three-chain structure. The calculation agrees well with the spectrum of oscillations obtained by the molecular dynamics method. Using the established mode dispersion, the heat capacity of Xe chains is calculated within the framework of the Einstein model. The calculation results are in good agreement with the experimental data in the temperature range of up to 35–40 K, which can be explained if we assume the presence of both one-dimensional and three-chain structures of Xe atoms adsorbed in the grooves between carbon nanotubes. The effect of temperature on the stability of Xe atomic structures on nanotubes has been studied, and it has been shown that one-dimensional structures start to defragment at temperatures higher than 60 K, whereas three-chain structures defragment at temperatures higher than 90 K.

The nonlinear dynamics of two magnetic elements with easy-plane magnetic anisotropy and ferromagnetic exchange interaction is considered in the framework of discrete Landau–Lifshitz equations. In the absence of damping, exact solutions of these equations are obtained for the proposed integrable dynamical system. The dynamics of the system, its frequency characteristics, and essentially nonlinear high-amplitude excitations, in particular, with a non-equal distribution of excitation between magnetic elements, have been fully investigated. The results of a theoretical study can be used in the analysis of dynamics of magnetic multilayers excited by a polarized current or a high-frequency field.

The Mayer group expansion method is extended on the low-temperature solids where quantum effects cannot be ignored and applied to the prediction of polymorphic transition line between cubic Fm3m and orthorhombic Pnma phases in the highly compressed ionic crystal of uranium dioxide. The temperature dependence of the transition pressure and volume changes are evaluated and the results are compared with existing experimental data and ab initio predictions.

This work presents the results of the analysis of the temperature dependence of the x-ray reflection intensity from solid heavy nitrogen in the ordered phase. The temperature dependence of the behavior of the orientational order parameter and mean square displacement of 15N2 molecules obtained from x-ray data is plotted. Based on the dependencies obtained, the orientational order parameter was determined at 0 K, which is 12% higher than the orientational order parameter obtained in theoretical works. It was found that the heavy nitrogen molecule “freely” rotates in the crystal at temperatures above 45 K.

Magnetic properties of a dense superfluid neutron matter (relevant to the physics in cores of magnetars, namely the strongly magnetized neutron stars) at supranuclear densities n > n0 (where n0 = 0.17 fm–3 is the saturation nuclear density) with generalized Skyrme effective forces (with three density-dependent terms) and with spin-triplet anisotropic p-wave pairing (similar to 3He-A in magnetic fields, i.e. with spin S = 1 and orbital moment L = 1 of anisotropic Cooper pairs of neutrons) in the presence of a superstrong magnetic field (exceeding the 1017 G) are studied within the framework of the non-relativistic generalized Fermi-liquid theory at zero temperature. The upper limit for the density range of a neutron matter is restricted by the magnitude 3n0 in order to avoid the account of relativistic corrections growing with density. The approximate general formula (valid for any parameterization of the Skyrme forces) is derived here analytically for the magnetic susceptibility (which contains additional correction depending nonlinearly on superstrong magnetic field H and on the density n) of a superfluid neutron matter in the limit of zero temperature. The obtained general formula for magnetic susceptibility is specified for the generalized BSk21 parameterization of the Skyrme forces and figures for corresponding values are plotted on the interval 1.5n0 ≤ n ≤ 3n0 and for superstrong magnetic fields 2⋅1017 G ≤ H ≤ 2⋅1018 G. It is established that the high-density ferromagnetic instability is removed in neutron matter with the generalized Skyrme forces (in particular, with the generalized BSk21 parameterization) not only in normal, but also in superfluid neutron matter with spin-triplet anisotropic p-wave pairing at supranuclear densities and in superstrong magnetic fields.

Electromagnetic wave refraction and reflection at the interface between vacuum and lossy metamaterial with zero real part of permittivity are analytically described by macroscopic classical electrodynamics. The analytical model is based on exact solutions of electromagnetic boundary problems. We have good reason to believe that in lossy metamaterial with zero real part of permittivity, the values of the magnetic field and energy flow are nonzero due to the crucial role of losses in epsilon-near-zero metamaterials. It is shown that the significant transmission of waves occurs for almost all incident angles. Moreover, the transmission coefficient increases with increasing loss for TE and TM wave polarizations. Numerical results are presented to show that the optical characteristics of waves at the interface of the metamaterial are highly sensitive to the losses and polarization of waves. The effect of the losses is most pronounced for transverse electric waves. The main contribution of this article is the characterization of the role of losses in the optical properties of epsilon-near-zero metamaterials that differs from some analogs known in the literature.

The absorption spectra of thin films (CsCl)1–x(CuCl)x were studied at T = 90 K in the spectral range 2–6 eV. From the analysis of the spectra, the formation of CsCu2Cl3 and Cs2CuCl3 compounds in the CsCl–CuCl system was created. The Cs2CuCl3 compound is stable only in a vacuum; in air, it apparently decomposes into CsCu2Cl3 with a disordered crystal lattice and CsCl. The exciton spectrum of both compounds is interpreted on the basis of transitions in the Cu+ ion. The one-dimensional character of excitons in CsCu2Cl3 and the two-dimensional character in Cs2CuCl3 were established.