Том 166, № 6 (2024)

As result of the development of sources of intense high-frequency radiation and the improvement of techniques for detecting charged fragments, experiments on multiple ionization of inner molecular shells with the momen- tum and charges of fragmentation products being registered in coincidence have become possible. In this paper, the dynamics of the disintegration of water molecule fragments resulting from interaction with intense X-ray radiation has been studied. The charge distribution of oxygen ions was calculated, Newton diagrams were con-structed for fragments — protons and the oxygen ion — at various charge states of the latter, and the kinetic energy release was determined. Calculations were performed using the original code [1] for parameters close to the experiment [2] conducted on EuXFEL in 2021.

Lattice regularization of gravity theory provides new opportunities for studying Big Bang physics. It is proved that in the 4D lattice gravity model studied here, there exists a high-temperature phase characterized by the vanishing of the mean energy-momentum tensor of matter and the collapse of space into a point. The existence of a low-temperature phase in the long-wavelength limit is also shown, whose geometric properties and dynamics correspond to known concepts: the Universe's expansion initially follows an exponential law and then smoothly transitions to a power-law regime.

Using X-ray diffraction analysis (XRD), Raman spectroscopy (RS), and quantum chemical calculations, the features of temperature behavior of thermally activated conformational disorder of terminal ethylene groups C₂H₄ of BEDT-TTF (or ET) molecules in crystals of quasi-two-dimensional organic conductor к-(BEDT-TTF)₂Cu[N(CN)₂]Cl were studied at temperatures from 112 K to 289 K. During slow cooling at a rate of –4 K/hour and steps of 10 K, crystal lattice parameters were measured and complete structural analysis was performed for characteristics temperatures. Crystal structure parameters show anomalous temperature behavior in the interval 175–250 К, in the same region an anomaly is observed in the behavior of intramolecular vibration frequencies of the ET molecule, which is associated with changes in the degree of conformational disorder. Based on the obtained structural data, the influence of the observed disorder on the electronic structure of the conducting layer was analyzed using quantum chemical modeling methods. In particular, the results of calculations using the semi- empirical extended Hückel method with a basis set optimized for the given system allowed determining the nature of electron density distribution both within the dimer and within the layer depending on the configuration of terminal ethylene groups. The main types of charge redistribution between molecules in the dimer ET₂ were identified. It is shown how the population of configurations and the degree of dimer polarization affect the stability of different types of charge ordering within the conducting layer and, ultimately, the conductive properties of the crystal.

The results of studying multilayer superconductor-ferromagnet-superconductor (SFS) Josephson junctions based on superconducting niobium and weak ferromagnetic alloy Pd_0.99Fe_0.01 are presented. A minimum in the dependence of critical current density on F-layer thickness is discovered, which is one of the signs of π-state realization with a negative sign of current-phase relation. The presence of 0-π-transition, i.e., transition between π-state and 0-state with increasing F-layer thickness, is also confirmed by the observation of reentrant temperature dependence of critical current at ferromagnet thickness of about 43 nm. Modeling predicts the second order number of the observed 0-π-transition.

Single crystals of pnictides BaFe_2−хNiхAs₂ with underdoped composition (x = 0.08) and overdoped compositions (x = 0.12, 0.14) were studied by tunneling spectroscopy in superconducting and normal states. The obtained I(V)- and dI(V)/dV characteristics of tunnel contacts reproducibly showed nonlinearity both below and above the critical temperature T_c, not directly related to superconducting properties. Its evolution with temperature and T_c along the doping phase diagram was studied, and possible causes of this nonlinearity existence are discussed.

The frequency dependence of vacancy movement hysteresis in a memristor closed on both sides under the influence of periodic electric current flowing through the memristor is considered. Based on an exactly solvable nonlinear model, an equation for hysteresis loops during the passage of rectangular current pulses with a duty cycle of 2 is obtained. The efficiency of vacancy charge transfer by current compared to their free diffusion is evaluated. It is shown that maximum efficiency is achieved at a specific memristor switching period, which depends on the amplitude of the applied current. Analytical asymptotics of this dependence and memristor resistance depending on the amplitude and period of the current passing through the memristor are obtained.

In studying the development of instabilities in a random medium, it is often assumed that memory in the medium is lost instantaneously at prescribed moments in time, while it is natural to assume that memory loss occurs gradually. This paper studies the effects arising from gradual memory loss. It turns out that long memory can increase the rate of instability development (increase the Lyapunov exponent). The connection between this effect and intermittency effects arising during the development of instabilities in a random medium is established. The study is conducted within the framework of a simple model proposed by Ya. B. Zeldovich for describing the development of instability arising under the action of curvature fluctuations during light propagation in a universe that is homogeneous and isotropic only on average.

New theoretical approaches have been developed for studying and quantitatively describing the elastic properties of cubic blue phases in cholesteric liquid crystals. Within the framework of the Landau–de Gennes theory, using the simplest blue phase O⁵ with spatial group (I432) as an example calculations of the bulk modulus and two shear moduli were performed depending on the chirality strength and temperature below the crystallization point from isotropic liquid. It is shown that the used approximations of rigid tensors and free helicoids give qualitatively similar results but differ noticeably quantitatively, therefore further experimental studies and numerical modeling of blue phase elasticity are necessary.