P.L. Kapitza Institute for Physical Problems

Results of the Rietveld X-ray diffraction analysis are presented for PbZr0.53Ti0.47O3, Pb0.95Sr0.05Zr0.53Ti0.47O3, PZT-19, and PZT-23 samples along with the results of studying their dielectric, piezo-, and pyroelectric properties. The samples are found to consist of a mixture of solid solutions having the perovskite structure with tetragonal (T), monoclinic (M), and rhombohedral (R) crystal lattices. Their weight fractions are 48T/39M/13R, 39T/61M, 49T/51M, and 72T/28M in the samples respectively. Main structural parameters of the phases are determined (unit cell symmetry and parameters of the phases, atomic coordinates and isotropic thermal displacements). The effect of the phase compositions of the samples on their electrophysical properties is discussed. Based on the results of the theoretical-group analysis, the conclusion is drawn that the observed differences in the ferroelectric and related (dielectric, piezoelectric) properties of the studied samples are due to: 1) concentration of monoclinic phase Cm, 2) structural parameters of the Cm phase.

Low-temperature paramagnets are a class of spin systems that remain in a disordered paramagnetic state down to the lowest temperatures despite the presence of noticeable spin-spin exchange coupling.The magnetic properties of these systems at low temperatures are due to collective spin excitations, and, in a magnetic field, such spin systems can demonstrate field-induced antiferromagnetic ordering.Magnetic resonance allows studying the details of the excitation spectrum in the paramagnetic low-field and ordered high-field phases of low-temperature paramagnets, revealing the fine structure of the spectrum of collective excitations, details of the interaction between excitations, changes in the excitation spectrum induced by the magnetic field, and the emergence of non-Goldstone modes of spin dynamics in high-field ordered phases.

In this experimental study we investigated the electron transport properties of non-equilibrium quasiparticles injected into superconducting aluminum at extremely low temperatures. The study deals with hybrid nanostructures represented by a T-shaped metal electrode (copper), an insulating tunneling layer (aluminum oxide), and a superconducting fork (aluminum). These nanostructures serve as the solid-state analogue of a two-slit optical interferometer. By imposing a constant bias voltage close to the superconducting energy gap, we observed the non-uniform dependence of the tunneling current on perpendicular magnetic field. This phenomenon is believed to originate from the coherent component of the quasiparticle transport. Our findings provide valuable insights into the behavior of quasiparticles in superconducting materials and may be useful for operation of various nanoelectronic devices containing interfaces with a superconductor.

Reply to the comment of P.L. Chapovsky to the paper “Symmetry approach in the problem of gas expansion into vacuum,” JETP 159, 794 (2021).

We report results of a multi-frequency (0.8-60 GHz) electron spin resonance study of the spin dynamics in the quasi-2D square lattice antiferromagnet Ba2MnGe2O7 both in antiferromagnetically ordered and paramagnetic phases. We directly observe two zero-field gaps in the excitation spectrum of the ordered phase, the larger one being due to easy-plane anisotropy, and the smaller one indicates the presence of fourth-order in-plane anisotropy probably related to the multiferroic properties of this compound. We observe effects of hyperfine interaction on the electron spin resonance spectra in the antiferromagnetically ordered state, which turns out to be comparable with in-plane anisotropy. The hyperfine field strength is found from the observed low-temperature electron spin resonance data. The spin dynamics of the paramagnetic phase is characterized by strong broadening of the ESR absorption line, which can be ascribed to the vortex dynamics of a 2D magnet.

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.

This review presents the main characteristics and mechanisms of operation of superconductor–insulator–normal metal–insulator–superconductor (SINIS) microwave detectors. An analysis of the detectors’ performance against a quantum detector and a photon counter is given. Methods for cooling a superconductor using normal metal traps and the role of electron cooling in optimizing the current response to terahertz radiation are discussed. Fabrication methods using shadow evaporation as well as magnetron sputtering are described.

Nematic superconductors are characterized by an apparent crystal symmetry breaking that results in the anisotropy of the in-plane upper critical magnetic field ${H}_{c2}$. The symmetry breaking is usually attributed to the strain of the crystal lattice. The nature and the value of the strain are debatable. We perform systematic measurements of the ${H}_{c2}$ anisotropy in the high-quality ${\mathrm{Sr}}_{x}{\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ single crystals in the temperature range 1.8 $\mathrm{K}<T<{T}_{c}\ensuremath{\approx}2.7$ K using temperature stabilization with an accuracy of 0.0001 K. We observe that in all tested samples the anisotropy is weakly temperature dependent when $T<0.8{T}_{c}$ and smoothly decreases at higher temperatures without any sign of singularity when $T\ensuremath{\rightarrow}{T}_{c}$. Such a behavior is in a drastic contradiction with the prediction of the Ginzburg-Landau theory for the nematic superconductors. We discuss possible reasons for this discrepancy.