Том 166, № 3 (2024)

The possibility to create multilayer dielectric structures (photonic crystals) performing integration and differentiation of the first and higher orders of the femtosecond pulse envelope has been shown theoretically. Suggested photonic crystals have a completely artificial photonic bandgap profile, which was achieved by solving the inverse problem of photonic crystals' optical response. The performance of these optical devices in a spectral range wider than an octave has been demonstrated.

The interference contribution to the optical conductance (total transmission) of a disordered sample is calculated. It is shown that wave interference in the medium is suppressed due to helicity-flip scattering events. As a result, when the cross-section of this process changes resonantly, as in the case of scattering by Mie particles near the first Kerker point, the spectral dependence of the interference contribution also becomes resonant. When waves propagate through a magneto-active medium, the applied magnetic field does not disrupt the interference of waves with given helicity but suppresses it if the helicity changes along different parts of the trajectory. This leads to a decrease in the interference contribution to conductance with increasing magnetic field. A similar phenomenon ― negative magnetoresistance ― is known as a consequence of weak localization of electrons in metals with impurities. It is found that with increasing magnetic field, the change in the interference correction to the optical conductance approaches a certain limit value, depending on the ratio of transport mean free path to helicity-flip scattering length. The possibility of controlling the transition to strong “Anderson” localization in the quasi-one-dimensional case (magneto-active waveguide) using the field is discussed.

The model analysis of hadron charge correlations in heavy ion collisions was performed for energies available at NICA collider. The balance functions are considered as characteristics of such charge correlations. They represent the probability densities for oppositely charged particles to fall within a certain rapidity and azimuthal angle intervals. It has been shown that observed at STAR experiment at RHIC collider dependences of rapidity widths on centrality of gold-gold collisions at center-of-mass energies   √SNN = 7.7 and 11.5 GeV per nucleon pair are reproduced by HYDJET++ model in the case of taking into account event-by-event conservation of electric charge for direct hadrons and finite values of isospin, strange and baryon chemical potentials.

Lateral spin devices with tunnel contacts Co_0.9Fe_0.1/MgO/InSb were fabricated using magnetron sputtering and maskless photolithography. The current-voltage characteristics and contact resistance, as well as the Hanle effect during the diffusion of polarized electrons between contacts, were measured. First-principles molecular dynamics calculations were performed to determine the band structure in supercells modeling the Co/MgO and MgO/InSb interfaces. It was shown that at the Co/MgO interface, a significant spin polarization arises for Bloch states of electrons. As a result, the probabilities of passing through the dielectric layer and through the ferromagnetic/dielectric and dielectric/semiconductor interfaces are different for these electrons. The height and width of the tunnel barriers were calculated based on an analysis of the current-voltage characteristics of the tunnel contacts. It was shown that a higher degree of polarization is achieved in tunnel contacts with higher barrier heights and higher resistance. It was also shown that at the MgO/InSb interface, due to the large difference in lattice parameters, there is a high likelihood of defect formation, which prevents achieving high polarization characteristics of the tunnel contacts.

The results of experiments on the effect of a magnetic field on the conductivity of superconductor — insulator — normal metal tunnel structures are analyzed at temperatures much lower than the critical temperature of the superconductor Tc and at low voltages at which the single-electron current Isingle is comparable to or less than the sub-gap Andreev current IA= In+Is. These two components of the Andreev current are associated with the diffusive motion of correlated pairs of electronic excitations in the normal and, accordingly, superconducting layers of the structure. With the orientation of the field perpendicular to the structure with lateral dimensions greater than the penetration depth, the transition from an inhomogeneous field distribution to a vortex structure is traced. At field orientations both in the plane of the structure and perpendicular to it, the single-electron current increases due to the influence of the field on the superconducting gap Δc. The conductivity due to the Andreev current In =kntanh(eV/2kTeff) decreases due to an increase in the effective temperature Teff. The decrease in the Is contribution is associated with a decrease of the gap. We do not know of any works that consider the influence of the magnetic field on this component of the tunneling current. It is shown that at low voltages, the so-called Dynes current, due to an imaginary addition to the gap energy due to the influence of defects in the superconductor, does not contribute to the conductivity of the tunnel structure.

The work examines a special behavior of the magnetic conductivity of metals that arises when chaotic electron trajectories appear on the Fermi surface. This behavior is due to the scattering of electrons at singular points of the dynamic system describing the electron motion in p- space, and caused by small-angle scattering of electrons on phonons. In this situation, the electronic system is described by a “non-standard” relaxation time, which plays the main role in a certain range of temperature and magnetic field values.:

The results of a spectroscopic study of the plasma created by a barrier discharge in low-pressure neon are presented, reflecting the evolution of the mechanisms of population of excited levels of the Ne* atom and Ne⁺* ion depending on the observation time relative to the beginning of the discharge. Analysis of the emission spectrum, correlated with measurements of the time dependences of the intensities of spectral lines, allows us to indicate four stages of spectrum evolution: direct population by electron impact in the active stage (discharge), followed by a stepwise population at its end with a transition, as the electron temperature relaxes, to recombination afterglow. The latter, depending on the gas pressure and the initial electron density, can also contain two stages – the initial one, with the predominance of the mechanism of collisional-radiative recombination of Ne⁺⁺ and Ne⁺ ions with electrons as the source of population of all excited levels of the Ne⁺* ion and neon atom observed in the experiment, and the final stage, the radiation in which is associated with the population of a limited group of levels due to the dissociative recombination of Ne₂⁺ molecular ions with electrons. The main attention in the work is paid to the population kinetics of the levels of configurations 2p⁵3p and 2p⁵4p of the neon atom.