JETP Letters最新文献

Single and polycrystalline samples of Mg_{2 – x}Mn_{1 + x}BO₅ (x = 0.0, 0.2, 0.4) oxyborates have been obtained for the first time by spontaneous crystallization from the solution–melt and through a solid-state reaction. X-ray diffraction studies have shown that compounds are crystallized with increasing manganese content in the ludwigite (space group Pbam)–hulsite (space group P2/m)–orthopinakiolite (space group Pbam) series and belong to the “3 Å wallpaper” borate family. A common property of materials is the presence of octahedral complexes (walls) consisting of manganese ions with a mixed valence at even crystallographic sites. The dc magnetization and specific heat of the Mg_{2 – x}Mn_{1 + x}BO₅ (x = 0.0, 0.2, 0.4) compounds have been studied for the first time. These studies have shown that cooling is accompanied by magnetic transitions, which are due to the ordering of several magnetic subsystems.

It has been shown that stray fields of a superconducting Pearl vortex can form bound states with high-order magnetic skyrmions due to orbital effects of an inhomogeneous magnetic field. By analogy with recent results for skyrmions with the topological charge |Q| = 1 [E. S. Andriyakhina, S. Apostoloff, and I. S. Burmistrov, JETP Lett. 116, 825 (2022)], the centers of high-order magnetic skyrmions in such bound states can be shifted with respect to the center of the superconducting vortex. It has been shown that ponderomotive forces acting on the simplest high-order magnetic skyrmions with the topological charge |Q| = 2 tend to form noncoaxial bound states.

In this study, the Ramsey spectroscopy of coherent population trapping resonances excited on the D₁ line of alkali metal atoms in miniature vapor cells has been studied theoretically and experimentally. The configuration of the field produced by two counterpropagating waves with opposite circular polarizations has been considered. A counterpropagating wave is formed as a result of reflection from a partially transmitting output mirror, while the signal from the initial wave transmitted through the mirror is detected. It is shown that such a scheme is characterized by the optimal mirror reflection coefficient, for which the short-term stability can be substantially improved relative to the standard scheme without the counterpropagating wave. The three-fold improvement of the short-term stability of the atomic clock based on the coherent population trapping resonance in a vapor cell with ⁸⁷Rb atoms has been demonstrated experimentally.

The possibility of the existence of the photovoltaic Hall effect, i.e., the transverse response of a two-dimensional system with a constant driving electric field acting in the plane of the system, to circularly polarized incident radiation near the phase transition of the system to the superconducting state from the normal phase at T > T_c is discussed. It is shown that the photovoltaic Hall effect can be caused by superconducting fluctuations in the regime where normal electrons do not contribute to this effect.

Narrowly divergent high-energy electron beam is experimentally demonstrated during the interaction of terawatt Ti:Sa laser radiation with a nitrogen gas-cluster jet at gas pressure corresponding to the boundary of the condensation region. A collimated electron beam with an energy of up to 10 MeV and a divergence of 10 mrad at a plasma concentration of ~10¹⁹ cm^–3 is obtained. The use of nitrogen instead of argon or krypton significantly improves the spatial (divergence) and energy (charge and spectrum shape) properties of the generated electron beam. The formation of clusters in a supersonic jet is observed and their composition is thermodynamically analyzed.

Relations have been derived to prove that field correlation functions for polarization and phase transformations of radiation states in quantum optics are equivalent in measurements.

The paper proposes an alternative scenario for the emergence of the baryon asymmetry of the Universe. This scenario is realized in the lattice gravity model associated with the Dirac field as follows. At ultrahigh temperatures of the Grand Unification order ({{T}_{c}} sim {{10}^{{18}}}) GeV and higher, the system is in a PT-symmetric phase. But when the temperature decreases, a phase transition to an asymmetric phase occurs, in which a non-zero tetrad appears, that is, space-time with the Minkowski metric, and the system’s wavefunction splits into two: (|,rangle = {text{|}} + rangle + ,{text{|}} - rangle ). The fields of tetrads in states ({text{|}} + rangle ) and ({text{|}} - rangle ) differ in sign. At the very first moment of time with a duration of the order of the Planck time, a transition of fermions between these states is possible. These transitions in different parts of space are not correlated with each other. Therefore, the final asymmetry of the fermion charge between these states is relatively extremely small and it is preserved in time, since the interaction of the states ({text{|}} + rangle ) and ({text{|}} - rangle ) ceases at times greater than the Planck time.

A conceptual model of a promising quantum accelerometer based on a two-mode atomic Bose–Einstein condensate has been proposed. Acceleration generates a specific difference in geometric phases between the condensate modes, which shifts the interference pattern of matter waves. The modes have ring configurations, in the plane of which the measured acceleration vector lies. The homogeneity of the potentials of the ring configurations is interrupted by additional localized potentials generated by defects. Under the variation of the parameters of appropriately located defects with a certain structure, the wavefunctions of the condensate modes acquire geometric phases that differ in the presence of acceleration. Calculations performed for ring configurations of the condensate of ⁸⁷Rb atoms with a radius of 0.25 mm has showed that the proposed scheme can detect a microgravity of ~10^–6–10^–7 g.

Features of the generation of a highly ionized plasma from a tip cathode after the electrical breakdown of a millimeter air discharge gap at atmospheric pressure have been studied using picosecond laser probing at a wavelength of 532 nm. It has been found that the transformation of a micron-sized cathode spot to a growing spark channel is accompanied by the formation of a spherical plasma region in the base of the spark channel in the near-cathode region. The electron density in this region, which is about 100 μm in diameter, decreases to 3 × 10¹⁹ cm^–3 in the center and increases to (5–6) × 10¹⁹ cm^–3 in its shell with a thickness of about 20 μm. It has been shown that the growth of the subsequent spark channel is governed by a strong ionization front formed at the boundary of the expanding spherical plasma region in 1 ns after the gap breakdown. It has been assumed that the formation of the spherical plasma region in the near-cathode region affects the subsequent development of the microstructure of the electric spark.

Studies of the laser-induced ultrafast processes in thin films are of significant importance for the development of microelectronics. These processes include the heating of an electron subsystem, relaxation and transport of the absorbed energy, and generation and propagation of picosecond acoustic waves. In view of this circumstance, to study the dynamics of variation of the differential reflection coefficient ΔR(t)/R₀ of a 73-nm-thick Ni film on a glass substrate, pump–probe measurements have been performed in this work with the synchronous detection of a ΔR(t)/R₀ signal. High absorbed fluences up to 11 mJ/cm² have been reached by increasing the pulse-repetition interval t_cool of heating (pump) pulses. An increase in t_cool makes it possible to better cool the film after heating. As a result, record temperatures T_e ≈ 3 kK and T_i ≈ 1 kK and stresses up to 7 GPa have been reached for the first time to the best of our knowledge. These high values have allowed the observation of nonlinear effects for the first time in experiments with synchronous detection.