Volume 118, Nº 9-10 (11) (2023)

Исследования на Нуклотроне в ОИЯИ указывают на наличие ранее неизвестной резонансо-подобной структуры в двухфотонном спектре масс в области 300-400 МэВ/ c 2, наблюдаемой в ядро-ядерных взаимодействиях. Целью данной работы является поиск таких структур в двухфотонном спектре масс в мезон-ядерных взаимодействиях при импульсе 7 ГэВ/ c на установке Гиперон-М ускорительного комплекса У-70. Установлено ограничение сверху на отношение сечения образования неизвестных резонансныхструктур к сечению рождения η-мезона ρ(R→2γ/η→2γ ) < 3.2 × 10 на уровне достоверности 95 %.

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.

Мы устанавливаем непосредственное соответствие между вольт-амперными характеристиками джозефсоновского контакта с высокой прозрачностью в режимах заданного тока и заданного напряжения. Мы показываем, что наличие субомической диссипации при подщелевых напряжениях и температурах приводит к линейной зависимости среднего напряжения V от заданного тока I , когда последний превосходит критический ток Ic. Это существенно отличается от корневой зависимости V ∝ I - Ic вомическом пределе. Наши предсказания сравниваются с недавними экспериментальными данными.

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.

Предложена концепция сенсора электромагнитного излучения ( nonlinear kinetic inductance sensor - NKIS) на нелинейной кинетической индуктивности. Идея сенсора основана на расходимости кинетической индуктивности Lk dq/dI (пq - импульс сверхпроводящих электронов, I - сверхток) гибридного сверхпроводник/нормальный металл (SN) мостика при токе I∗ < Idep (Idep - ток распаривания гибрида) и температуре T ∗ много меньшей критической температуры гибрида Tc. Это позволяет получить большое изменение разности фаз δφ вдоль SN мостика в режиме заданного тока при I ≃ I даже в случае малого роста электронной температуры. Возникновение δφ сопровождается изменением тока и магнитного потока через связанное сверхпроводящее кольцо, что может быть измерено с помощью сверхпроводящего квантового интерференционного прибора (СКВИДа). В некотором смысле предложенный сенсор является сверхпроводниковым аналогом сенсора на краю резистивного перехода (transition edge sensor - TES), чья работа основана на наличии большой производной dR/dT (R - сопротивление) вблизикритической температуры сверхпроводника Tc. Так как при I ≃ I SN мостик находится в бесщелевомрежиме, у него отсутствует нижняя граница для частоты детектируемого элeктромагнитного излучения. Расчеты показывают, что такой сенсор может работать в однофотонном режиме и детектировать одиночные фотоны с частотой ν 10 ГГц. В работе обсуждается, что нетривиальная зависимость I(q) SN мостика может быть также использована в детекторах непрерывного электромагнитного излучения, сенсорах тока и магнитного поля.