JETP Letters最新文献

The evolution of the optical properties of a 25-nm-thick nickel film on a glass substrate excited by a subpicosecond terahertz pulse with a field strength of 11 MV/cm has been studied by femtosecond interference microscopy with a time resolution of 10^–13 s. The measurements of the complex reflection coefficient and the permittivity in the visible range of the spectrum indicate the non-equilibrium heating of the electron subsystem of nickel to several thousands of degrees, which is accompanied by the induced increase in reflection at the initial time of irradiation and by the subsequent melting after 5–10 ps. Scanning electron and atomic force microscopy studies of the morphology of the modified surface have indicated the local melting of the nanofilm and its delamination from the substrate at this field strength.

In this paper, we applied a deep neural network to study the issue of knowledge transferability between statistical mechanics models. The following computer experiment was conducted. A convolutional neural network was trained to solve the problem of binary classification of snapshots of the Ising model’s spin configuration on a two-dimensional lattice. During testing, snapshots of the Ising model spins on a lattice with diagonal ferromagnetic and antiferromagnetic connections were fed to the input of the neural network. Estimates of the probability of samples belonging to the paramagnetic phase were obtained from the outputs of the tested network. The analysis of these probabilities allowed us to estimate the critical temperature and the critical correlation length exponent. It turned out that at weak anisotropy the neural network satisfactorily predicts the transition point and the value of the correlation length exponent. Strong anisotropy leads to a noticeable deviation of the predicted values from the precisely known ones. Qualitatively, strong anisotropy is associated with the presence of oscillations of the correlation function above the Stefenson disorder temperature and further approach to the point of the fully frustrated case.

The superconducting state in heterostructures containing layers of a superconductor and a ferromagnet, which is split into domains, has been studied taking into account the long-range electron–electron interaction in the ferromagnetic layer. The critical temperature and spatial distribution of the order parameter in different heterostructures have been calculated. Various types of spin valves have been examined, including a valve based on solitary reentrant superconductivity in asymmetric superconductor/superconductor/superconductor systems. A shift of the minimum has been observed in the dependence of the critical temperature of the superconductor/superconductor/superconductor system on the thickness of the ferromagnetic layer due to the presence of a domain structure. A state with alternating signs of the phase of the superconducting order parameter in one of the superconducting layers against the background of domain walls has been obtained. In superconductor/superconductor/superconductor systems, the alternation of the phase sign is also possible at the edge of one of the ferromagnetic layers because of the alternation of the magnetization direction. The possibility of using the sensitivity of the order parameter phase to magnetic inhomogeneities to create a controllable 0–π Josephson junction is discussed.

A possibility of the formation of a two-frequency light bullet in the second harmonic generation regime is analytically studied taking into account the focusing Kerr nonlinearity. It has been demonstrated that a stable light bullet with an upper limit on its intensity, as well as lower limits on time duration and aperture, can be formed under conditions of phase and group matching and the absence of group velocity dispersion at the second harmonic frequency.

Transmission spectra of TiS₃ single crystal whiskers in the infrared and optical bands have been studied at various light polarizations in the temperature range from room to liquid helium. The absolute absorption coefficients have been determined. Previously unknown phonon modes have been observed in the far infrared region. The study of the temperature dependence of the band gap width ({{mathcal{E}}_{{text{g}}}}) has shown that it increases by 50 meV under cooling from 300 to 5 K. The comparison of spectra measured at different polarization directions indicates that the optical gap is anisotropic. A 1.28-eV absorption peak has been detected below ~150 K and has been attributed to the excitation of excitons.

We examine statistics of fluctuations of the light beam intensity at its propagating in a turbulent atmosphere. We are interested in the probability of relatively large values of the beam intensity. The model of a phase screen is considered. We find the tail of the probability density function characterized by the stretched exponent with power 7/12. Conditions of realizing the tail are established. The general picture is discussed.

The magnetoresistance of a well-characterized bulk FeSi sample has been studied. It is shown that after some complicated behavior at temperatures below 6 K, the magnetoresistance of FeSi, becomes a regular function of temperature and magnetic field. Then, the magnetoresistance passes a maximum at about 12 K and gradually decreases, approaching slightly negative values and then zero. Thus, the observations suggest the existence of the negative component of magnetoresistance, which appears at about 12 K and finally defines the negative values of both transverse and longitudinal magnetoresistance of FeSi at high temperatures. The n-egative component of magnetoresistance may be related to the topological features of the chiral structure of FeSi.

We consider heavy quark contributions to the polarized Bjorken sum rule. We found good agreement between the experimental data and the predictions of analytic QCD. To satisfy the limit of photoproduction, we use new representation of the perturbative part of the polarized Bjorken sum rule, recently proposed.

The new version of the SANCphot integrator has been developed for fast and stable numerical calculations up to two loops for polarized light-by-light scattering. One-loop modules based on the helicity formalism with massive particles and two-loop modules with massless particles inside the loops are used. The presented study is driven by the potential of polarized photon beams to probe the high energy region. This study is a contribution to the research program of the CEPC project being under development in China.

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.