JETP Letters最新文献

Dynamic disorder in metal halide perovskites is driven by thermal structural fluctuations of cross-linked octahedra leading to a broadband central peak in the low-frequency region of electronic Raman scattering spectrum. In this work, a temperature dependence of the Raman central peak in metal halide perovskite CsPbBr₃ is experimentally demonstrated. The results of this study hold promise for the development of edge-cutting remote temperature sensors.

The effect of the variation of the spin current on the magnetic susceptibility of a magnonic waveguide in the form of a “ferromagnet–normal metal” heterostructure is investigated. Based on the Landau–Lifshitz–Gilbert model with the current term in the Slonczewski–Berger form, which describes the magnetization dynamics including the spin moment transfer, expressions are obtained for the real and imaginary parts of the magnetic susceptibility in the geometry of surface spin waves in the damping mode. The resulting model correctly approximates experimental data demonstrating an increase in the amplitude of spin waves propagating in a YIG/Pt heterostructure. It is shown that an increase in the spin current leads to an increase in the resonance frequency of spin waves and in the magnetic susceptibility tensor components in resonance. The results of this study can be used to design waveguides for spin waves with controllable losses and high-sensitivity magnetic field sensors.

The paper presents the results of studying the vibrational spectrum of the PbNi_1/3Nb_2/3O₃ (PNN) crystal using Raman scattering in the temperature range from 100 to 650 K, including the region of the “diffuse phase transition” with a maximum permittivity at ({{T}_{m}} = 150{kern 1pt} ) K at a frequency of 10 kHz. Polarized light scattering spectra in PNN are similar to those observed in a number of studied relaxor ferroelectrics with a perovskite structure (AB{kern 1pt} '{kern 1pt} B{kern 1pt} ''{kern 1pt} {{O}_{3}}). Analysis of the temperature evolution of phonon modes allowed us to identify special points in the dynamics of the PNN crystal lattice at ({{T}_{1}} = 280{kern 1pt} ) K and ({{T}_{m}} = 150{kern 1pt} ) K. It is shown that anomalies in the temperature behavior of optical phonons in the vicinity of ({{T}_{1}}) can be associated with the dynamics of polar nanoregions, the nature of which changes from dynamic to static. In the studied temperature range, a sequence of phase transformations is proposed for PNN crystals.

Within the Rabi quantum model, it has been shown theoretically that a two-level atom ultrastrongly coupled to an electromagnetic field generates or absorbs photons. Photons can be generated if the field is initially in the vacuum state. Under certain initial states of the atom + field system, the absorption of photons is possible in the field mode in the ultrastrong atom–field coupling regime. If the atom is initially in the ground (unexcited) state and the field is in the vacuum state, photons can be generated under resonance condition ω_a ≈ ω_f or ξ ≡ ω_a/ω_f ≈ 1, where ω_a and ω_f are the atomic transition and field frequencies, respectively, in the ultrastrong coupling regime. At the negative detuning when ξ ( ll ) 1 or ω_a ( ll ) ω_f, Rabi oscillations of the average number of photons ({{langle hat {n}rangle }_{t}}) with (0 leqslant {{langle hat {n}rangle }_{t}} leqslant {{n}_{{max }}} gg 1) are observed in the case of the ultrastrong coupling with the atom–field coupling constant (tilde {g} equiv {text{|}}g{text{|/}}{{omega }_{{text{f}}}} sim 1); in this case, the population of the excited atomic state is P_e(t) ≈ 0.5. At a large positive detuning when ξ ( gg ) 1, photons are not generated, i.e., (langle hat {n}rangle approx 0), and the atom remains in the initial state, i.e., P_e(t) ≈ 0. The statistics of photons in the generation regime is nearly chaotic: the variance of photons is much larger than the level of the coherent field state (i.e., is super-Poisson). Field photons are absorbed without the excitation of the atom in the ultrastrong coupling regime in the case of the coherent initial state of the field ((langle hat {n}(t = 0rangle > 0)) for certain positive detuning values. In this case, the field becomes sub-Poisson.

A system of equations has been proposed for a monochromatic weakly nonlinear light wave in a Kerr medium. This system is equivalent up to the third order in electric field to the known equation ({kern 1pt} {text{curl}},{text{curl}}{mathbf{E}} = k_{0}^{2}[{mathbf{E}} + alpha {text{|}}{mathbf{E}}{{{text{|}}}^{2}}{mathbf{E}} + beta ({mathbf{E}} cdot {mathbf{E}}){mathbf{E}}{text{*}}]), but the new equations are much more convenient for numerical computation. Optical fields with small structures of two or three wavelengths have been simulated using this system. It has been found that a stable self-focused light beam (a two-dimensional vector soliton) in some parametric domain is possible even without modification of nonlinearity. “Inelastic” collisions between two such narrow beams with opposite circular polarizations have been calculated. Furthermore, examples of interacting optical vortices, spatial separation of the circular polarizations, and the Kelvin–Helmholtz instability have been given for defocusing nonlinearity.

The excess entropy ΔS with respect to the maternal crystal state has been determined from calorimetric data for 30 metallic glasses. It has been shown that the excess entropy in the supercooled liquid state ΔS_sql is a universal characteristic of a glass independent of its thermal treatment. Six parameters often used to estimate the glass-forming ability of supercooled melts have been calculated for the same metallic glasses. It has been shown that all six parameters increase with ΔS_sql and the glass-forming ability of supercooled melts increases with their structural disorder. A possible mechanism to implement this relation has been discussed.

A method has been proposed for photoinduced hyperthermia of pathogenic Gram-negative bacteria P. aeruginosa using Gd₂O₃:Yb micropowder. It is based on the possibility of laser excitation of anti-Stokes luminescence on ytterbium ions in the gadolinium oxide micropowder, which allows us, on the one hand, to heat the powder to the required temperature and, on the other hand, to accurately control the powder temperature using remote luminescent thermometry. It has been demonstrated that the long-term irradiation of the Gd₂O₃:Yb micropowder with 1035-nm nanosecond laser radiation changes the shape of anti-Stokes luminescence spectra associated with micropowder heating in the range from 27 to 63°C. The application of the proposed photoinduced hyperthermia method to a mixture of solutions of the Gd₂O₃:Yb micropowder and P. aeruginosa bacteria demonstrates a decrease in the bacterial population by 90%.

A number of open questions remain in the manipulation of the spins of colliding beams, which is a key aspect in the operation of polarized beam colliders such as the Nuclotron-based ion collider facility (JINR, Dubna, Russia) and the electron ion collider (BNL, United States). The spin transparency regime, which is the only realistic regime to control the deuteron polarization, has not yet been approved experimentally. With the existing configuration of the JINR accelerator complex, a pilot spin transparency experiment could be performed on a proton beam in the Nuclotron synchrotron. The dynamics of the proton beam polarization during the fast crossing of spin resonance guided by spin navigators based on regular orbit-steerer dipoles has been analyzed in this work. A scheme has been designed to compensate the coherent action of Nuclotron lattice imperfections on spin. In this scheme, the spin field induced by lattice imperfections is determined from the adiabatic deviation of spins in the resonance region, taking into account the synchrotron energy modulation. Integer-resonance strengths can be compensated down to the limits conditioned by orbital beam emittances. The numerical simulation of the proposed spin compensator has confirmed that the spin transparency regime in an imperfect Nuclotron lattice with a strongly distorted closed orbit can be experimentally verified.

The nuclear quadrupole resonance study of the electron-deficient substitution in the promising thermoelectric material FeGa₃ resulting in the poorly studied Fe_0.92Re_0.08Ga₃ and Fe_0.92Mn_0.08Ga₃ compounds has been carried out. The doping of compounds of this structure type promotes the study of the dependence of the thermoelectric characteristics on the electronic structure and finally makes it possible to increase the thermoelectric efficiency, which is very important for applications. Both compounds exhibit pronounced signatures of the formation of an additional acceptor band inside the main band gap, which is determined by rhenium and manganese substituent atoms. Nuclear quadrupole resonance spectra, as well as nuclear spin–lattice relaxation and its temperature evolution, are significantly different for the compounds under study. This difference is due to different statistical distributions of substituent atoms (predominant formation of homo- and heterogeneous dumbbells in the rhenium- and manganese-substituted compounds, respectively) caused by their outer electron shells.

The dependence of the superparamagnetic blocking temperature on an external magnetic field T_B(H) has been studied and analyzed for a nickel ferrite nanoparticle powder system in order to establish the influence of magnetic interparticle interactions on superparamagnetic blocking. The features of this system are: (i) a small particle size (~4–5 nm on average); (ii) a pronounced “core/shell” structure of particles, in which the magnetic moment of a particle is formed by a ferrimagnetically ordered core, while the spins of the surface layer, about 1 nm thick, do not contribute to this magnetic moment. The random anisotropy model, which describes the influence of magnetic interparticle interactions on the T_B value in the external field, is used to reproduce the experimental dependence T_B(H) obtained by static magnetometry. The analysis has demonstrated strong magnetic interactions in the studied system, which are manifested in a sharp decrease in the T_B value in the weak-field region, and has made it possible to quantitatively estimate the intensity and energy of magnetic interparticle interactions, as well as to determine the magnetic anisotropy constant of individual particles (without the influence of magnetic interparticle interactions). The role of the subsystem of surface spins, which, according to the imaginary part of the magnetic susceptibility, exhibits signatures of collective behavior, is discussed as a possible source of magnetic interparticle interactions.