Vol 118, No 9-10 (11) (2023)

Studies at the Nuclotron in JINR indicate the presence of a previously unknown resonance-like structure in the two-photon mass spectrum in the region of 300–400 MeV/c², observed in nucleus–nucleus interactions. The goal of this work is to search for such structures in the two-photon mass spectrum in meson–nuclear interactions at a momentum of 7 GeV/c at the Hyperon-M experiment of the U-70 accelerator complex. An upper limit has been established on the ratio of the cross section for the formation of unknown resonance structures to the cross section for the production of η">$\eta$-meson ρ(R→2γ/η→2γ)<3.2×10−3">$\rho (R_{\to 2\gamma }\text{/}{\eta }_{\to 2\gamma })<3.2\times {10}^{-3}$ at the 95% confidence level.

Optically active (bright) and optically inactive (dark) quartet S = 3/2 spin color centers including a negatively charged Si vacancy have been identified in silicon carbide using high-frequency electron nuclear double resonance on the nuclei of the 13C isotope, enhanced by a tenfold increase in its content. The alignment of populations of spin levels is optically induced in a bright center promising for quantum technologies, whereas the populations of spin levels in a dark center, which is an isolated negatively charged Si vacancy V-Si, correspond to a Boltzmann distribution and do not change under optical excitation.

Nonequilibrium phenomena in planar Josephson SNS nanostructures, where the superconductor (S) is Nb and the normal metal (N) is Cu or Au, have been studied experimentally. Using additional N electrodes attached to the S banks of the Josephson SNS junction, transport measurements have been performed at low temperatures with the injection of quasiparticles with the use of local and nonlocal connection schemes. The charge-imbalance relaxation length in niobium at temperatures much lower than the superconducting transition temperature has been determined experimentally for the first time.

We establish a direct relation between the I–V curves for highly transparent Josephson junctions in the voltage- and current-biased regimes. We demonstrate that the presence of sub-Ohmic dissipation at subgap voltages and temperatures yields the linear dependence of the average voltage V¯">$\overline{V}$ on the bias current I exceeding the critical one Ic">$I_c$, in contrast to the square root dependence V¯∝I−Ic">$\overline{V}\propto \sqrt{I-I_c}$ in the Ohmic limit. Our predictions are compared with recent experimental findings.

Ab initio calculations have been performed to study the dynamic stability of a new MgCl₂ monolayer and the formation of point defects in it. The possibility of using the MgCl₂ monolayer in Li- and Na-ion batteries has been analyzed. It has been shown that the MgCl₂ monolayer has the dynamic stability but can contain point defects. These point defects can improve the adsorption capability of the MgCl₂ monolayer with respect to Li and Na atoms. The results obtained in this work indicate that the MgCl₂ monolayer is a promising material for application in Li- and Na-ion batteries.

Dielectric spectra of SrTiO₃ and SrTiO₃:Mn single crystals have been studied in the frequency range of 10‒3000 cm^–1 and in the temperature range of 5–297 K using time-domain terahertz spectroscopy and Fourier-transform infrared spectroscopy. A comparative analysis of the experimental results made it possible to detect a significant broadening of the absorption lines corresponding to the Slater and Last phonon modes, while the parameters of the Axe mode when replacing Ti with Mn (2 at %) stay invariant. This effect is associated with an enhance in structural disorder in the cation subsystem (B-sublattice) of the SrTiO₃ crystal. It has been established that doping with Mn ions reduces the antiferrodistortive phase transition temperature by about 20 K, but hardly affects the character of the temperature dependence of the parameters of a ferroelectric soft mode at temperatures of about 60–297 K. It has been found that an additional excitation with the frequency below the frequency of the ferroelectric soft mode should be taken into account for an appropriate model description of the dispersion of the permittivity of SrTiO₃:Mn in the terahertz frequency range. The results obtained in this work indicate that dielectric relaxation in the SrTiO₃:Mn crystal is due to thermally activated hops of Mn atoms between displaced (noncentral) crystallographic sites; i.e., the mechanism of radiofrequency relaxation in SrTiO₃:Mn is hopping rather than polaronic, which is also actively discussed in the literature.

The analysis of experimental data on the structure of hydrocarbon pellet clouds on the LHD stellarator has allowed one to estimate the relative contributions of neutral and plasma shielding at the ablation of macroparticles (pellets) in a high-temperature magnetized toroidal plasma. A method for the self-consistent calculation of the pellet ablation rate, the characteristic size of the pellet cloud, and the electron density in its singly ionized part including neutral gas and plasma shielding is described. This calculation for polystyrene pellets injected into the LHD plasma gives the results that agree with the experimental data obtained during the early ablation phase, when the ablation rate is determined by thermal electrons and the contribution of the superthermal component of the hot plasma to ablation can be neglected.

Experimental syntheses of two iron polyhydrides FeHx(I) and FeHx(II) have been carried out in diamond anvil cells by laser heating of metallic iron to temperatures of about 700 and 2000 K at pressures of 178 and 195 GPa, respectively. The initial sample is an iron plate enriched in the Fe-57 Mössbauer isotope placed in ammonia borane (BH3NH3). The electronic properties of FeHx compounds have been studied by measuring the electrical resistance R(T) at high pressures (180–216 GPa) in the temperature range of ~8–300 K. Based on the obtained R(T) data, two superconducting phases of FeHx compounds with the maximum critical transition temperatures Tc ≈ 25.0 and 27.7 K have been identified. It has been found that with increasing pressure, the temperature Tc in both hydrides increases linearly with the coefficients dTc/dP ~ 0.063 ± 0.001 K/GPa and 0.056 ± 0.003 K/GPa for the FeHx(I) and FeHx(II) phases, respectively. Superconductivity in iron hydrides revealed by the measured resistance R(T) has been confirmed by a number of additional methods.

The problem of mechanical vibrations of an aerogel attached to an elastic wire in superfluid ³He is solved for the case, where the aerogel is also in a superfluid state. The hydrodynamic boundary conditions at the aerogel surface formulated in this work allow one to explain the anomalously rapid increase in the frequency of mechanical vibrations of the system on cooling. The found relation between the phase jump at the aerogel boundary and the superfluid current flowing across the boundary suggests the Josephson character of such current.

The concept of nonlinear kinetic inductance sensor (NKIS) of electromagnetic radiation is proposed. The idea is based on divergency of kinetic inductance Lk∼dq/dI">$L_k\sim dq\text{/}dI$ (ℏq">$\hslash q$ is a momentum of superconducting electrons, I is a supercurrent) of hybrid superconductor/normal metal (SN) bridge at current I*<Idep">$I\text{*}<I_{\text{dep}}$ (Idep">$I_{\text{dep}}$ is a depairing current of the hybrid) and temperature T* much smaller than critical temperature Tc">$T_c$. It makes possible to have large change of phase difference δϕ">$\delta \varphi$ along SN bridge in current biased regime at I≃I*">$I\simeq I\text{*}$ even for small electron temperature increase. Appearance of δϕ">$\delta \varphi$ is accompanied by the change of the current and magnetic flux through the coupled superconducting ring which could be measured with help of superconducting quantum interference device (SQUID). In some respect proposed sensor may be considered as a superconducting counterpart of transition edge sensor (TES) those work is based on large derivative dR/dT">$dR\text{/}dT$ (R">$R$ is a resistance) near Tc">$T_c$. Because at I≃I*">$I\simeq I\text{*}$ SN bridge is in gapless regime there is no low boundary for frequency of detected electromagnetic radiation. Our calculations show that such a sensor can operate in single photon regime and detect single photons with frequency ν≳">$\nu \gtrsim$ 10 GHz. We argue that the nontrivial dependence I(q)">$I(q)$ of SN bridge could be also used in detectors of continuous electromagnetic radiation, current and magnetic field sensors.