Vol 163, No 5 (2023)

The nonlinear absorption and photoluminescence of CdTe/CdSe nanotetrapod colloids have been studied by the pump–probe method for the case of single-photon nonresonance excitation of excitons. A competition between the short-wave and long-wave shifts of the peak of photoluminescence associated with an indirect electron–hole transition, which is observed with increasing excitation radiation intensity, has been found and explained. The former shift is associated with an increase in the one-dimensional exciton radius after the exciton state occupation, and the latter shift may be attributed to the charge-induced Stark effect and local heating of nanotetrapods as a result of electron–phonon interaction at nonresonance excitation of the system.

We present the results of tuning and calibration of the detector electronics in the signal digitization mode. The goal of the experiment is to search for a possible sterile neutrino signature in tritium beta-decay. The read-out electronics work in direct oscilloscope mode, which requires to optimize time frame the with the goal to minimize noise and energy resolution. We use a 7-pixel silicon drift detector (SDD) and a CMOS charge sensitive preamplifier with very low integration capacitor. Amplifier forms a slowly rising output shape and operates in pulse-reset mode. The 125 MHz ADC digitizes the signals. Using calibration data from Fe55 and Am241 gamma sources we check triangular and trapezoid digital filters to obtain the best noise and energy resolution performance. We are also examining the option to differentiate the output signal.

The static state of a black hole in interaction with dark matter is considered in the synchronous coordinate system. Just as in Schwarzschild coordinates, in synchronous coordinates there exists a regular static spherically symmetric solution of the system of Einstein and Klein–Gordon equations that describes the state of matter extremely compressed by its own gravitational field. There is also no constraint on the mass. There also exist two gravitational radii with the boundary conditions at which the solutions are not unique. In contrast to Schwarzschild coordinates, in synchronous coordinates the determinant of the metric tensor and the component g11(r) do not become zero at the gravitational radii. In synchronous coordinates, in contrast to Schwarzschild coordinates, in the spherical layer between the gravitational radii the signature of the metric tensor is not violated. In synchronous coordinates the Einstein and Klein–Gordon equations are reduced to a system of the second (rather than fourth) order. The solutions were obtained analytically, so that no numerical calculations were required. The gravitational mass defect in the λψ4 model was determined. The total mass of matter turns out to be thrice the Schwarzschild mass determined by a remote observer when compared with Newtonian gravity.

We consider the problem of determining the permittivity and the electrocaloric effect in the model of a ferroelectric ceramics grain. We assume that a grain consists of a spherical ferroelectric core coated with a dielectric shell and placed into a dielectric matrix. The transition layer thickness is assumed small as compared to the grain size. The dependence of the polarization on the electric field in the core is given by the nonlinear Ginzburg–Landau equation. The polarization reversal is induced by a change in the electric field that is considered uniform at large distance from the grain. The electrostriction effect in the core–shell–matrix three-phase system produces an elastic field described by linear equations. To take into account the effect of domain walls on the physical characteristics of the ceramics in the given model, we propose that the Kittel–Mitsui–Furuichi approach be used. The proposed computational algorithm makes it possible to refine the dependence of the number of domains on the spherical grain size. The electrocaloric effect in the grain is represented by the combination of the primary and secondary effects that appear due to ordering of dipole moments of the ferroelectric with the perovskite structure; by way of example, we consider the barium titanate ceramics. For this material, we report on the results of calculations of the dependences of the permittivity and individual electrocaloric effect components on the grain size.

Experimental investigations of antiferromagnetic topological insulator MnBi2Te4 have shown that the energy gap in samples may vary in a wide range. Since the energy gap is a key parameter of this system when used in developing new functional electronic devices, the reason for variation of the MnBi2Te4 energy gap at the Dirac point and its possible interrelation with magnetic interactions are matters of great importance and call for thorough analysis. To elucidate factors influencing the energy gap, we analyzed the variation of the electronic structure of the given topological insulator with surface van der Waals gap. Calculation data have shown that the energy gap at such structure modifications may vary in a wide range from 80–88 meV to 4–5 meV because of an intense spatial redistribution of topological surface states between septuple-layer MnBi2Te4 blocks with oppositely directed Mn magnetic moments. Our results suggest that the spatial localization of topological surface states is a primary factor governing the value of the energy gap, this localization being strongly dependent on structure modifications on the crystal surface.

We study statistical properties of the passive scalar advection in a 2D flow that consist of a steady-state shear flow and a relatively weak smooth random component taking into account the effects of finite weak diffusion. The model is closely related to the dynamics of passive scalar transfer inside coherent vortices emerging as a result of an inverse cascade in 2D turbulence. We analyze both the decay of the passive scalar and the problem with continuous supply of the scalar to the system. In both cases, the passive scalar distribution exhibits strong intermittence, which can be indicated with single-point moments calculated in this study.

It has been shown that the formation of autoionization states makes the dominant contribution to inelastic energy loss and to ionization in keV atomic collisions, i.e., at velocities lower than the velocities of atomic electrons. Scaling laws have been proposed to calculate the cross sections for the formation of vacancies in inner K and L electron shells of colliding atoms. A model has been proposed to relate ionization processes and the observed inelastic energy losses. Auger transitions in a short-lived quasimolecule formed by two atoms approaching each other have been studied. The nature of the continuous component in electron spectra emitted in collisions has been determined. It has been shown that the excitation of autoionization states determines the stopping cross sections for keV atoms in matter.