JETP Letters最新文献

It is shown that the experimentally detected features in the low-temperature behavior of the magnetization in an external magnetic field perpendicular to the layers of manganese ions of the topological antiferromagnet MnBi₂Te₄ are due to quantum effects induced by the off-diagonal nature of the trigonal component of the crystal field. In this case, the anomalous increase in the magnetization of the material before the spin-flop transition, as well as after it in the phase of “collapsed” sublattices, is explained by the suppression of contributions from quantum effects. The comparison of the results of the theoretical analysis with experimental data has made it possible to refine the parameters of the effective spin model of MnBi₂Te₄ and to establish the important role of the noted trigonal component.

Dispersion relations in a metal with a commensurate helical magnetic order are considered in the framework of one- and two-dimensional tight-binding models. The generalized Bloch theorem for translations combined with spin rotations, together with the Born–Karman periodic boundary conditions, leads to the appearance of multisheet dispersion curves (surfaces). It is demonstrated that the resulting band structure is topologically nontrivial, which can lead to a spin textured Fermi surface and cause transport anomalies.

An analytical model has been developed to describe the electron transport in semiconductor photocathodes exposed to microwave radiation from radiofrequency photoguns. The considered model, whose applicability framework is presented, makes it possible to obtain an analytical expression for the photocurrent profile, which potentially allows a more accurate simulation of the operation regime of radiofrequency photoguns for generating ultrashort (pico- and subpicosecond) electron bunches. The dependence of photocurrent fronts on the model parameters has been considered and discussed. The main directions for the development of the model have been outlined.

A method to describe the hidden mass effect or dark matter has been proposed on the basis of a new general solution of the Poisson equation for the gravitational field strength in a continuous self-gravitating medium. This solution is a consequence of the theory of space and matter alternative to the general relativity. Conditions have been derived to distinguish between the cases where the obtained solution describes the classical Newtonian gravitational field and the cases where this solution leads to the hidden mass effect. The representation obtained for the gravitational field strength has been analyzed within the model of the dynamic equilibrium of disk galaxies and the possibility of describing the observed properties of the hidden mass effect within this approach has been discussed.

Using a method of low frequency Raman scattering, hydrated planar samples of phospholipid bilayers are studied at room temperature. It has been demonstrated that a relaxation response, the spectral shape of which corresponds to a wide distribution of relaxation times in the picosecond range, is manifested in the subterahertz range. The spectral susceptibility of the relaxation response is described by a power function with an exponent of 0.25, is the same for gel and fluid phases of phospholipid bilayers, and does not depend on the degree of saturation of hydrocarbon tails of different phospholipids. The subterahertz relaxation response can be considered as an elementary relaxation event, which precedes slower relaxation processes such as lateral diffusion and changes in the thickness or curvature of a phospholipid bilayer.

Exactly forty years ago, the spin superfluidity and Bose–Einstein condensation of magnons in superfluid antiferromagnetic ³He-B were discovered. In this work, the existence of spin superfluidity and phase slippage in an yttrium iron garnet film at room temperature is demonstrated using the optical Faraday effect. The s-patial distribution of the phase and amplitude of the spin precession under the conditions of magnon Bose‒Einstein condensation are studied by varying the pump phase difference between two strip lines exciting magnons.

The cross section for the neutron-induced fission of ²³⁷Np nuclei in the neutron energy range of 0.3–500 MeV has been measured using the time-of-flight spectrometer of the GNEIS neutron complex at the Petersburg Nuclear Physics Institute, National Research Center Kurchatov Institute. The ²³⁷Np(n, f) fission cross section has been measured with respect to the ²³⁵U(n, f) fission cross section and fission fragments have been detected by low-pressure position-sensitive multiwire proportional counters. The data obtained have been compared to the previous experimental results and to estimates from various evaluated data libraries.

Flexoelectricity in a macroscopically unpolarized multidomain ferroelectric is considered. It has been shown that the flexoelectric moduli are modified due to the piezoelectric effect in individual domains. The perturbation theory has been developed, where the effect appears in the third order. The estimate of the effect for lead titanate in the isotropic approximation has shown that corrections to the flexoelectric moduli f₁₁₁₁ and f₁₁₂₂ are comparable with their initial values and depend only on the initial value of f₁₂₁₂. The correction to f₁₂₁₂ is small, which allows one to use the perturbation theory.

In this article a new method is proposed for estimating the mass composition of cosmic rays in individual events with energies above (1.25 times {{10}^{{19}}}) eV. It is based on a joint analysis of experimental data and simulation results obtained using the QGSjet-II.04 model for muons with threshold energy ({{E}_{mu }} = 1.0 times cos theta ) GeV in air showers with zenith angles up to 60°. The data from ground-based and underground scintillation detectors of the Yakutsk EAS array were used. Separate groups of nuclei and other primary particles were found.