JETP Letters最新文献

Double half-Heusler alloys represent a novel promising class of materials for applications, e.g., in thermoelectric energy converters. In this work, the electronic thermoelectric properties of five MgXY₂Z₂ (X = Zr/Hf, Y = Pd/Pt, Z = Bi/Sb) compounds of this alloy class with the previously predicted low lattice thermal conductivity have been investigated for the first time. It has been shown that the Seebeck coefficients of MgHfPd₂Sb₂ and MgTiPd₂Sb₂ are among the highest in double half-Heusler alloys. The dependences of the Seebeck coefficient and power factor on the chemical potential at different temperatures and carrier densities have been analyzed, and the relationship between these dependences and the peculiarities of the electronic structure of the considered compounds has been revealed.

Oscillations in the cross sections for single-electron charge-exchange of fast nonrelativistic positive ions on a hydrogen molecule are considered. The charge-exchange cross sections for the protons and alpha particles at fixed orientations of the hydrogen molecule are calculated as functions of the energy of the incident particles using the representation of the impact parameter in the Brinkman–Kramers approximation with normalized capture probabilities. The cross sections averaged over all orientations of the molecule are also presented. The results are compared with the available experimental data.

The electric polarization induced by a magnetic field H in Nd₃Ga₅SiO₁₄ noncentrosymmetric trigonal paramagnetic single crystals has been detected. In low fields, it is quadratic in H and its components in the basal ab plane are described by two magnetoelectric susceptibilities α₁ and α₂. The polarization along the trigonal c axis is manifested only starting from the fourth-order terms ~H⁴. In high magnetic fields at low temperatures, when the magnetic moments of Nd³⁺ are saturated, the polarization qualitatively changes its field dependence to nearly quasilinear for all crystallographic directions and increases strongly (up to 250 μC/m² at 5 T along the c axis). The effects observed in Nd₃Ga₅SiO₁₄ have been quantitatively described using the spin Hamiltonian of the Nd³⁺ ion in local low-symmetric (C₂) sites taking into account the magnetoelectric interaction allowed by symmetry. Magnetoelectric invariants nonlinear in H that make it possible to describe the observed the field, temperature, and angular dependences of the polarization using several magnetoelectric parameters have been constructed in terms of the local susceptibilities of Nd³⁺ ions taking into account the nonequivalence of their magnetization.

The temperature behavior of the topological index C₁ of the chiral superconducting d + id phase of a two-dimensional single-band model on a triangular lattice has been studied. It has been found that the temperature dependence of the topological index fundamentally changes at carrier densities, at which the nodal points of the Brillouin zone approach the Fermi contour of the normal phase. It has been shown that the topological index C₁ in a wide temperature range is close to C₁ = 4 (–2) when the nodal points are located far inside (outside) the Fermi contour. However, when nodal points approach the Fermi contour, these values are maintained only at low temperatures, and values close to C₁ = 1 in a wide temperature range. It has been assumed that such a topological crossover in the system under consideration can lead to significant changes in edge states in a similar open-boundary system.

The possibility of the appearance of a light–dark spatiotemporal soliton in the second-harmonic generation mode with the normal group velocity dispersion at the fundamental frequency in the absence of such a dispersion at the second harmonic frequency has been demonstrated theoretically. This object has the form of a dark two-color soliton with respect to time and coordinate in the direction of propagation and is light with respect to the transverse (spatial) coordinates.

The work presents a multiparametric analysis of the effect of antibacterial nanogels based on nano- and (sub)microparticles of silver, copper and selenium on single- and multicomponent biofilms of gram-positive bacteria Staphylococcus aureus, Staphylococcus epidermidis, as well as gram-negative bacteria Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Nanogels are based on glycerol, silicone oil and Vaseline, which are low-costing biocompatible materials, suitable for use in wound dressings. The active components are bactericidal Ag, Cu, and Se nanoparticles. Nanogels and their effect on the bacterial biofilms were studied by standard microbiological inoculations, as well as Fourier transform infrared spectroscopy methods, followed by principal component analysis. After the treatment of biofilms with nanogels, a decrease in the bacterial population up to 99% was observed. Principal component analysis demonstrated the ability to differentiate viable from nonviable bacteria.

Absolute measurements of the X-ray spectrum of a plasma formed by intense femtosecond laser radiation on the surface of a solid target in a wide range of interaction parameters with varying the intensity and contrast of a laser pulse have been carried out. The energy distribution of the photon flux from the plasma created on the metal target in the range from 0.1 keV to 1 MeV and higher has been determined for the first time in a single experiment. Using the data obtained, physical processes in the interaction region have been analyzed. The temperatures of background and hot plasma electrons have been estimated. The role of these electron in the generation of the photon flux and the efficiency of laser radiation conversion into various ranges has been studied. A close relationship between the observed results and the contrast and peak intensity of laser radiation has been found.

In this work, the spectral properties of the terahertz radiation of a spintronic emitter based on the Co(2 nm)/Pt(2 nm) ferromagnet/heavy metal heterostructure and the periodic system of strips made of it (period from 4 μm to 1 mm) have been experimentally studied. Two main mechanisms that determine the terahertz spectrum of such emitters are demonstrated. The first of them is observed both in a continuous multilayer film and in a periodic lattice. In this mechanism, due to the interference of signals from different spatial regions of the emitter, the amplitude of the wave decreases with an increase in the angle between the normal to the film and the direction of radiation propagation, and the characteristic scale of this decrease depends on the wavelength. As a result, the increase in this angle is accompanied by the redshift of the spectral amplitude maximum of radiation. The second mechanism is possible only in the periodic system of strips. It occurs as the fact suppression of terahertz radiation due to the charge accumulation at the boundaries of the strips when periodic lattices with a short period are magnetized along the strips. This effect is more significant for longer wavelengths and is therefore accompanied by a blueshift of the spectral maximum. The mechanisms studied in this work will make it possible to create spintronic emitters of terahertz radiation with a given position of the spectral amplitude maximum of terahertz radiation.

The conductivity of nominally undoped single-crystal diamond films grown epitaxially by chemical vapor deposition on a heavily boron-doped p⁺-type diamond substrate has been studied. The conductivity of the films has been determined by the boron acceptor impurity. The temperature dependence of the conductivity in the temperature range of 300–500 K obeys the activation law, but the activation energy significantly exceeds the ionization energy of boron acceptors of ε_i = 0.37 eV. It has been found that the acceptors are strongly compensated. This leads to the appearance of a random potential with a large amplitude of γ ≈ 0.2 eV, leading to a large increase in the activation energy ∼ε_i + γ. The reason for the appearance of the strong random potential has been attributed to the self-compensation of boron impurities by nitrogen atoms during the chemical vapor deposition growth of diamond films on the heavily doped substrate.

Time-resolved absorption spectroscopy with subnanosecond time resolution requires sources of white light with short or ultrashort durations, which can be synchronized with other laser systems. Using a near-infrared femtosecond laser source, a supercontinuum with a high spectral brightness (~10 pJ/nm), a high pulse-to-pulse stability of about 2–5%, and a long-term (several hours) stability has been generated in the spectral range of ~450–750 nm. These supercontinuum characteristics have been achieved by operating in a divergent beam, which makes it possible to avoid multiple filamentation, to stabilize the spectrum (halving fluctuations and a wider energy stability range), and to broaden it by changing the dynamic balance between Kerr focusing, plasma defocusing, and diffraction. Time resolution has been achieved by means of a specially developed electronic delay system based on field-programmable gate arrays, which has made it possible to achieve subnanosecond time resolution in a wide time window (up to several milliseconds). This technique has been successfully tested in experiments to study the dynamics of silicon ablation under nanosecond laser impact.