JETP Letters最新文献

Resonant inelastic X-ray scattering (RIXS) spectra at Fe ({{L}_{{2,3}}}) absorption edges are used to study the electronic structure of SrFeO_2.46 and SrFeO_2.82. The RIXS spectra of SrFeO_2.82 in comparison with those of SrFeO_2.46 are characterized by less intense elastic recombination peaks and less pronounced inelastic spectral features, which is associated with a lower degree of localization of ({{d}^{4}} + {{d}^{5}}underline L ) states compared to ({{d}^{5}}) states. The inelastic scattering features of the RIXS spectra are attributed to d–d excitations. At higher excitation energies, where the continuum-excited fluorescence becomes dominant, the X-ray emission spectra are in good agreement with the measurement results of the photoelectron spectra of the valence bands of both SrFeO_2.46 and SrFeO_2.82. It is shown that Tanabe–Sugano diagrams can be used to interpret the RIXS spectra of the SrFeO_2.46 ferrite with trivalent iron ions located both in octahedra and in tetrahedra of oxygen ions.

Directional superluminescence on a large number of spectral lines in the wavelength range of 310–470 nm has been obtained during the filamentation of 950-nm femtosecond radiation from a Ti:sapphire laser in carbon dioxide. The lines have been identified as transition lines between the vibrational levels of electron-excited A²Π_u and X²Π_g states of CO(_{2}^{ + }) ions. The effect of the pressure on the radiation spectrum has been studied and mechanisms of the observed phenomenon are discussed.

The spin and optical properties of two main types of spin defects (nitrogen vacancy (NV) centers and divacancies) in an isotopically purified crystal 6H-²⁸SiC at different temperatures of the sample have been studied using the high-frequency electron paramagnetic resonance method and the luminescence analysis. It has been established that the ratio of the intensity of electron paramagnetic resonance signals from divacancies to the intensity of signals from NV defects decreases monotonically with an increase in the crystal temperature from 40 to 140 K, and signals from divacancies are no longer observed at temperatures above 140 K. The analysis of the optical characteristics of defects under the variation of the crystal temperature and the determination of activation energies have shown that all types of color centers, regardless of their position in the crystal lattice and the type of symmetry (C_1h and ({{C}_{{3{v}}}})), have a mechanism for thermal quenching of luminescence. The obtained results indicate that electron qubits based on NV centers and divacancies can be simultaneously located within one silicon carbide matrix, with the subsequent selective initialization, processing (evolution), and reading of the state of a certain single center.

The frequency dependence of the proton conductivity of ice and water is theoretically investigated in a wide frequency range. The electric field of the inhomogeneous distribution of proton current carriers and their finite mass are taken into account. The first factor is responsible for the difference in the behavior of the transverse and longitudinal conductivities, the appearance of two different characteristic times, and an additional increase in the conductivity at frequencies above the Debye frequency. Physically, the difference in the behavior of the transverse and longitudinal conductivities is due to the collective oscillations of current carriers in the second case. At the same time, the finite masses or inertial properties of current carriers lead to a faster asymptotic decrease in the conductivity as the frequency tends to infinity and to the elimination of the violation of the sum rule characteristic of the conventional Debye frequency dependence. The obtained results are compared to the experiment.

The effect of proton transfer in water has been studied by the molecular dynamics method with the ReaxFF potential, which supports the dynamic formation of bonds and makes it possible to simulate proton transfer. The self-diffusion coefficients of water and the diffusion coefficients of the H₃O⁺ and OH^– ions in the water have been studied along the water saturation curve from the triple to the critical point and in a wide pressure range from 1 to 300 MPa. A linear dependence of diffusion coefficients on temperature in Arrhenius coordinates has been obtained, and the transfer energies of molecules and ions have been examined.

A new type of flexoelectric effect is discovered as the nucleation of magnetic bubble domains under the action of local pressure on the surface of an iron garnet film. The comparison with a similar electric field-induced effect indicates the analogy between the physical consequences of the action of an electric field and a mechanical stress gradient on a magnetic sample.

An analytical theory of nonlinear generation of large-scale magnetic turbulence in an anisotropic magnetoactive plasma in a quasilinear approximation disregarding the direct nonlinear interaction of individual harmonics has been constructed. It has been shown that anomalous particle collisions caused by scattering on small-scale fluctuations of developed Weibel turbulence lead to the instability of long-wavelength harmonics stable in the linear approximation. The nonlinear growth of such harmonics at a given anisotropy of the particle velocity distribution, which is consistent with short-wavelength turbulence at the saturation stage and possible anisotropic injection of particles, occurs in the superexponential regime and corresponds to the explosive instability. The increase law of the large-scale field has been found and the critical explosion time has been determined.

The hypothesis of the factorization of the double nuclear modification factor in relativistic heavy ion collisions is tested for different types of final-state hadrons within the HYDJET++ model. The results demonstrate that this factorization holds reasonably well at moderately high transverse momenta, provided that the effects of double parton scattering can be small or neglected.

In black hole thermodynamics, entropy is non-extensive. This entropy obeys the composition rule which coincides with the composition rule in the non-extensive Tsallis–Cirto (delta = 2) statistics. Here we extend this approach to the thermodynamics of white holes. The entropy of the white hole is negative as follows from the rate of macroscopic quantum tunneling from black hole to white hole. The white hole entropy is with the minus sign the entropy of the black hole with the same mass, S_WH(M) = –S_BH(M). This reflects the anti-symmetry with respect to time reversal, at which the shift vector in the Arnowitt–Deser–Misner formalism changes sign. This symmetry allows one to extend the Tsallis–Cirto entropy by adding a minus sign to the Tsallis–Cirto formula applied to white hole. As a result, the composition rule remains the same, with the only difference being that instead of entropy it contains the entropy modulus. The same non-extensive composition rule is obtained for the entropy of the Reissner–Nordström black hole. This entropy is formed by the positive entropy of the outer horizon and the negative entropy of the inner horizon. The model of the black hole formed by black hole atoms with Planck-scale mass is also extended to include the negative entropy of white holes.

We calculate the away-side hadron-triggered modification factor ({{I}_{{AA}}}) in (AA) collisions at RHIC and LHC energies for scenarios with and without quark–gluon plasma formation in (pp) collision. We find that for both scenarios theoretical results for ({{I}_{{AA}}}) agree well with the available data for 2.76 TeV Pb + Pb and 0.2 TeV Au + Au collisions. We make predictions for ({{I}_{{AA}}}) in 7 TeV O + O collisions that are planned at the LHC. Our results show that measuring ({{I}_{{OO}}}) in the whole centrality interval and at small centrality (( lesssim 5)%) may give information on the presence of jet quenching in (pp) collisions.