JETP Letters最新文献

A theory of high-frequency hydrodynamic flows of two-dimensional electrons in nanostructures with a low defect density and edges with various imperfections is developed. It is shown that a resonance in high-frequency viscosity coefficients leads to a dependence of the sample impedance on a magnetic field with a sharp singularity, the character of which depends on the edge type: complete adhesion of the fluid to the edges corresponds to a narrow high resonance, while increasing fluid slip near the edges leads to a strong broadening of the peak and a decrease in its amplitude, followed by its disappearance. Thus, the type of boundary conditions is an important factor determining the shape of high-frequency two-dimensional electron flows. Possible explanations within the developed model for the anomalous magnetophotoresistance observed in ultrapure graphene samples and GaAs quantum wells are discussed.

Surface electromagnetic waves in graphene in a static magnetic field have been theoretically studied in the hydrodynamic regime. The antisymmetric conductivity tensor of graphene is obtained taking into account the spatial dispersion arising due to the effect of hydrodynamic pressure. It is shown that the spatial dispersion leads to a uniaxial anisotropy of the graphene conductivity in addition to the gyrotropy of graphene arising in the magnetic field. Dependences of the frequency of magnetoplasmoacoustic waves on the dispersion, magnetic field, and electron density are calculated. At large wave vectors, the magnetoplasmon is transformed into electronic magnetosound with a nearly linear dependence of the frequency on the wave vector. It is shown that the magnetic gyrotropy of graphene does not hybridize the polarization states of magnetoplasmons in the quasielectrostatic regime.

The method of extrapolation of variational calculation results to large model spaces based on an ensemble of artificial neural networks is applied to the study of properties of nuclei with A = 6. Using ab initio No-Core Shell Model (NCSM) calculations with the realistic Daejeon16 NN interaction, we extrapolate the energies and root-mean-square (rms) radii of the point-proton, point-neutron, and point-nucleon (matter) distributions in the ground states of ({}_{{}}^{6}{text{He}}) and ({}_{{}}^{6}{text{Li}}) nuclei. We perform pioneering extrapolations of energies and rms radii of resonant states, in particular, of the ({}_{{}}^{6}{text{Be}}~) ground state and of the excited states (0⁺, 1) and (3⁺, 0) of ({}_{{}}^{6}{text{Li}}).

The interaction of neutrinos with an energy of up to 55 MeV from the Spallation Neutron Source (SNS) accelerator with a promising ¹²⁷I detector at the Oak Ridge National Laboratory (United States) has been studied. The resonance structure of the charge-exchange strength function S(E) has been calculated taking into account high-lying resonances, and the effect of this structure on the cross section σ(E) for the accelerator neutrino capture by the ¹²⁷I nucleus has been examined. The influence of the Gamow–Teller resonance GTR-1 and the second new higher resonance GTR-2 on the energy dependence of the cross section σ(E) has been analyzed. The effect of the high-lying analog resonance AR-2 has also been taken into account for the first time. It has been found that the contributions of GTR-1, GTR-2, and AR-2 to the calculated cross section σ(E) are from 60% to ≈80%, about 12%, and ≤10%, respectively. The contribution of high-lying resonances to the (ν, n) and (ν, 2n) neutrino capture cross sections with neutron emission and the formation of the ¹²⁶I and ¹²⁵I isotopes, respectively, has been analyzed. The comparison of the cross sections for the interaction of accelerator neutrinos calculated by different methods with experimental data has shown coincidence at energies below the neutron separation threshold E_x < S_1n and strong discrepancy at higher energies, which is difficult to explain. A new measurement of cross sections at energies E_x > S_1n is needed.

The values of the Hubble constant obtained from the data on the early and late Universe differ by 10%, which is about five standard deviations. The DESY collaboration data can help solve this problem. These data are very consistent with the previously obtained refinement of the standard recombination theory, and the value of the Hubble constant H₀ = 73.5 km/s/Mpc from measurements in the late Universe.

The radiation of a quantum particle in a thermostatic electromagnetic field with a nonzero photon density in the presence of a strong Stark interaction between the particle and field is considered. New fundamental effects—the suppression of radiation by the Stark interaction in an intense broadband field and an additional “decay” shift in the energy of the decaying level, which is different from the Lamb and Stark level shifts—have been established. A new effect of the suppression of radiation is complementary to the effect of suppression of the polarization relaxation of the quantum particle in a squeezed field, which is discovered earlier by Gardiner. The new effect can occur independently of the effect established by Gardiner.

In this study, the effect of γ-radiation from typical commercial medical sources based on X-ray tubes and linear accelerators on the electrostatic properties of radiosensitizing gold nanoparticles located in a tissue-like medium has been evaluated numerically using a Monte Carlo simulation in the Geant4 software package. It has been shown that for realistic radiation doses, a significant fraction of gold nanoparticles of up to ~10^‒1 can, at least temporarily, change their surface charge sufficiently to convert anionic gold nanoparticles into cationic ones, which can lead to cytotoxic effects.

A physical mechanism of the generation of an ultraviolet resonant dispersive wave in a hollow waveguide is proposed based on a nonlinear phase modulation process with equal group velocities of an optical infrared soliton and an ultraviolet radiation pulse. An analytical expression for the wavelength of the resonant dispersive wave is obtained. Experiments confirming the proposed mechanism are conducted.

The laser writing of microstructures in the bulk of fused silica exposed to tightly focused laser pulses has been analyzed in detail. The self-consistent simulation of a single laser pulse exposure and the formation of electron–hole plasma together with the experimental data has made it possible to verify the mechanism of plasma self-organization and relate it to the mechanisms of defect accumulation in dense plasma regions under multipulse exposure. The dependence of the parameters of the induced microstructures on the wavelength, duration, energy, and exposure of the laser pulse has been investigated. The role of plasma-electron-induced defocusing effects, as well as the contribution of radiation self-focusing, has been analyzed. The heating of the material by the end of the laser pulse has been estimated.

The results of an experiment on the two-photon excitation of exciton states in krypton cryocrystals by the fifth harmonic of 209-nm laser radiation have been presented. It has been shown that the two-photon excitation mechanism allows reaching a density of 10¹⁶ cm⁻³ of free excitons with an excitation energy of ~8.4 eV at a focal radiation intensity of ( approx {{10}^{{11}}}{kern 1pt} ) W/cm². The observed broad photoluminescence line arising from the relaxation of excited exciton states covers the (3{text{/}}{{2}^{ + }}(8.4{kern 1pt} ;{text{eV}}) to 5{text{/}}{{2}^{ + }}(0.0)) low-energy nuclear isomeric transition in ²²⁹Th. Analytical estimates showing that two-photon laser generation of exciton states in noble gas crystals can be used as a new method for the excitation of the nuclear isomeric state of thorium at a pump intensity of ~10¹¹ W/cm² have been provided.