卷 166, 编号 5 (2024)

Polarization spectra of a two-level system in a polychromatic field were obtained in two cases: using the rotating wave approximation and without using this approximation. The obtained spectra were compared using two indicators: the average deviation across the entire frequency range and the deviation at the transition frequency. Both indicators allow quantitative assessment of the distortion in polarization spectra introduced by the application of the rotating wave approximation. The dependencies of the above indicators on key model parameters were obtained – on the central frequency, detuning, and spectral width of the applied polychromatic field. The obtained dependencies allow evaluating the applicability limits of the rotating wave approximation for a given level of acceptable distortions in the polarization spectrum.

An explanation is provided for why the Bruggeman equation is unsuitable for calculating the effective permittivity of a composite material containing a filler with negative permittivity. Formulas have been derived for calculating the effective permittivity of a composite containing spherical nanoparticles of filler with negative permittivity. These formulas can be used in producing composite materials with specified permittivity when metal nanoparticles are used as fillers in composites. The existence of a non-monotonic “resonant” dependence of the effective dielectric permittivity on the concentration of filler nanoparticles is predicted in these cases.

The heating of a molecular cloud by photons emitted by a primary black hole (PBH) located inside the cloud is considered. For graphite and silicate dust particles, the dependence of dust temperature on the distance from PBH is derived, along with the emission spectrum of dust particles. The obtained spectrum is compared with the sensitivity of the Millimetron space observatory for various values of concentration and size of dust particles and different PBH masses.

Results of measuring the properties of zirconium diboride ZrB₂ in the temperature range of 2500– 5000 K are presented: enthalpy, heat of fusion, heat capacity, specific electrical resistivity. Data for the liquid phase were obtained for the first time. The study was conducted using microsecond current pulse heating – Lebedev's “exploding conductors” method on sintered plates of ZrB₂. The measured melting onset temperature of the diboride, 3400–3440 K, agrees with the B-Zr phase diagram. It was established that at 3000 K the heat capacity C_p = 2 J/g•K is twice as high as the extrapolated low-temperature reference data, and in the liquid phase, there is a monotonic decrease in C_p from 2 to 1.5 J/g•K (at 5000 K). To explain the discrepancies, a hypothesis about the determining role of Frenkel defects in the melting region of rapidly heated substance is used.

. The resonant spectrum of dislocation paths in a NaCl(Ca+Ni) crystal has been measured under ultra- low crossed magnetic fields, the constant Earth field and alternating pump field. The movement is caused by spindependent transformation of impurity stoppers on dislocations, leading to their depinning and relaxation displacements in the field of internal stresses. The spectrum of resonant pump field frequencies is interpreted in terms of hyperfine interaction of electron pairs at impurity centers and surrounding Cl ligands. The spectrum is compared with previously obtained spectra: of microhardness on the same crystal and of dislocation paths in NaCl(Ca) crystal. Similarities and differences among the three spectra provide establishing the relative role of Ca and Ni impurities in the observed processes.

An evolution equation for polarization (electric dipole moment density) has been derived for type II multiferroics, where polarization is proportional to the vector product of cell ion spins. A regime is considered in which the main evolution mechanism is exchange Coulomb interaction, modeled by the Heisenberg Hamiltonian. The obtained polarization evolution equation contains spin density and nematic tensor density, which appears as an anticommutator of spins for particles with S = 1 and higher (for particles with spin S = 1/2 it degenerates into particle concentration). Also, to construct a closed model of spin and polarization evolution in multiferroics, equations for the above-mentioned physical quantities were obtained. The spin-current model is justified using the momentum balance equation and spin evolution equation, derived from the microscopic many-particle Pauli equation taking into account spin-orbit interaction. To analyze the mechanism of electric dipole moment formation proportional to the vector product of magnetic ion spins, the spin-current model was used, within which the relationship between the proportionality coefficient and the exchange integral was obtained. The mean-field approximation is used in the work, where the many-particle wave function of the ion system is approximated by the product of single-particle functions.

We experimentally investigate Josephson current between two 5 µm spaced superconducting indium leads,coupled to a NiTe2single crystal flake, which is a type-II Dirac semimetal. Under microwave irradiation, wedemonstrate a. c. Josephson effect at millikelvin temperatures as a number of Shapiro steps. In addition to theinteger (n= 1,2,3,4, ...) steps, we observe fractional ones at half-integer values n= 1/2,3/2,5/2and 7/2,which corresponds to πperiodicity of current-phase relationship. In contrast to previous investigations, we donot observe 4πperiodicity (disappearance of the odd n= 1,3,5, ... Shapiro steps), while the latter is usuallyconsidered as a fingerprint of helical surface states in Dirac semimetals and topological insulators. We argue,that our experiment confirms Josephson current through the topological hinge states in NiTe2: since one canexclude bulk supercurrent in 5 µm long Josephson junctions, interference of the hinge modes is responsible forthe πperiodicity, while stable odd Shapiro steps reflect chiral character of the topological hinge states.

The interest in the ferroelectric non-volatile memory as a candidate for low power consumption electronic memories was raised after the discovery of ferroelectricity in hafnium oxide. Doping by different elements of hafnia films allows improving their ferroelectric properties. In this work, the transport experiments are combined with the simulations to study the evolution of ferroelectric properties and the mean distance between oxygen vacancies during the endurance of hafnium-zirconium oxide in metal-ferroelectric-metal structures to study the impact of different metal electrodes.

For atmospheric air as a mixture of molecular gases in thermodynamic equilibrium, an algorithm is presented for calculating the density of atoms and molecules in the case of separation of dissociative transition regions for each component. The result is compared with an approximation where the partial pressures of nitrogen and oxygen are temperature-independent. Ionization equilibrium at temperatures below 7000 K occurs through the formation of molecular ion NO⁺, and at higher temperatures, the formation of atomic ions of oxygen and nitrogen dominates. It is shown that at pressures around atmospheric, with accuracy higher than 10%, electron-excited states of atoms can be neglected in the analysis of ionization equilibrium up to complete ionization of air. For the analysis of air plasma in the lightning conducting channel, the use of results and experimental data shows that the passage of the main electric current during the return stroke phase is temporally separated from the subsequent expansion of the heated channel. It is shown that the plasma temperature of the conducting channel between adjacent flashes, as well as before the passage of the main electric current, is approximately 4 kK. This temperature is maintained by small external electric fields.

The scenario of low-threshold decay of an ordinary microwave with a frequency corresponding to the second harmonic of electron cyclotron resonance, leading to the excitation of two electron Bernstein waves two- dimensionally localized in a large-scale coherent structure in a rarefied plasma, has been investigated. Using the proposed model, estimates for the threshold of this nonlinear phenomenon were obtained for ASDEX-Upgrade and Wendelstein 7-X facilities, as well as in a model experiment on a linear device.