卷 125, 编号 1 (2017)

The theory of transport of fluctuating double-frequency optical radiation in a gas of three-level atoms in the presence of rf radiation forming a closed excitation circuit has been generalized. The theory is based on the quantum kinetic equations for the atomic density matrix, which are solved together with the wave equations for classical electromagnetic fields. After averaging over the radiation fluctuation ensemble, a transition is made to equations for atomic-field correlation functions and transport equations for the spectral density of fields.

We have studied the peculiarities of diffraction of light in magnetic photonic crystals at large values of magnetooptical activity parameter and modulation depth. We have considered the case of an arbitrary angle between the directions of the external static magnetic field and the normal to the layer. The problem has been solved by the modified Ambartsumyan layer summation method. It has been shown that the given system is nonreciprocal with respect to not only circular, but linear polarizations also. In this case, a new type of nonreciprocity is observed (namely, the relation R(α) ≠ R(–α) holds, where R is the reflection coefficient and α is the angle of incidence). It has been demonstrated that in the case of oblique incidence, there appears a new photonic forbidden band that is not selective relative to the polarization of incident light. We have detected strong dependences of reflectance, absorbance, transmittance nonreciprocity, and other characteristics on the angle between the direction of the external static magnetic field and the normal to the layer boundary. Such a system can be used as a controllable polarization filter and a mirror, as well as a source of circular (elliptic) polarization, a controllable optical diode, and so on.

A new device is designed: it consists of a nanocell (NC) filled with Rb atom vapors and placed in a vacuum chamber. When the pressure in the chamber changes in the range 0–1 atm, the NC thickness is smoothly varied in the range L = 140–1700 nm, which is caused by the pressure-induced deformation of thin garnet windows in the chamber. The pressure dependence has excellent reproducibility even after many hundreds of cycles of letting in of air and its complete pumping out from the chamber. The accuracy of setting required thickness L is much better than in the wedge-gap NCs to be moved mechanically that were used earlier. The processes of Faraday rotation (FR) of a polarization plane, resonance absorption, and fluorescence are studied using the D₁-line narrow-band continuous laser radiation when the thickness changes from L = λ/2 (398 nm) to L = 2λ (1590 nm) at a step λ/2. The FR signal is shown to be maximal at L = λ/2 and 3λ/2 and to have the minimum spectral width (≈60 MHz). At L = λ and 2λ, the FR signal is minimal and has the maximum spectral width (≈200 MHz). The resonance absorption demonstrates the same oscillating behavior; however, the effect in the case of FR is much more pronounced. The oscillating effect is absent for resonance fluorescence: its spectral width and amplitude increase monotonically with L. The detected effects are explained and possible applications are noted.

The collision centrality dependence of the yields per unit rapidity dN/dy along with their ratios for various hadrons produced in Au+Au collisions at different collision energies have been studied within the framework of unified statistical thermal freeze-out model (USTFM) taking into account both longitudinal and transverse hydrodynamic flows. Bulk freeze-out properties in terms of the thermal parameters, temperature and mid-rapidity baryon chemical potential at chemical freeze-out, obtained within the proposed model, which are in agreement with experimental data. The extracted chemical freeze-out temperature is found to depend weakly on the collision centrality. It is also found that this temperature is almost independent of the collision energies considered in this work. The closeness of the freeze-out temperature to the predicted phase-transition temperature suggests that the chemical freeze-out happens near hadronization. Furthermore, the dependence of the mid-rapidity chemical potential on the collision energy at different centralities, as well as the centrality dependence of the mid-rapidity size of the system in terms of the transverse size of the system, has been studied at the RHIC. The effect of resonance decay contributions has also been taken into account.

We have analyzed the neutrino events recoded in the deep-water neutrino experiment NT200 in Lake Baikal in five years of observations toward dark dwarf spheroidal galaxies (dSphs) in the southern hemisphere and the Large Magellanic Cloud (LMC). This analysis completes the series of works based on NT200 data in the search for a dark matter annihilation signal in astrophysical objects. We have found no significant excess in the number of observed events relative to the expected background from atmospheric neutrinos in all tested directions, in 22 dSphs and the LMC. For a sample of five selected dwarf galaxies we have performed a joint analysis of the data by the maximum likelihood method. We have obtained a correspondence of the observational data to the null hypothesis about the presence of only background events and established 90% confidence-level upper limits for the annihilation cross sections of dark matter particles with a mass from 30 GeV to 10 TeV in several annihilation channels both in the joint analysis of the selected sample of galaxies and in the analysis toward the LMC. The strongest constraints at a level of 7 × 10^–21 cm³ s^–1 have been obtained for the direction toward the LMC in the channel of annihilation into a pair of neutrinos.

Our previously proposed approximation involving both the first and second terms of the expansion of the vertex function is generalized to the system of two interacting wavefields of different physical nature. A system of self-consistent equations for the matrix Green’s function and matrix vertex function is derived. On the basis of this matrix generalization of the new self-consistent approximation, a theory of magnetoelastic resonance is developed for a ferromagnetic model, where the magnetoelastic coupling parameter ε(x) is inhomogeneous. Equations for magnetoelastic resonance are analyzed for one-dimensional inhomogeneities of the coupling parameter. The diagonal and off-diagonal elements of the matrix Green’s function of the system of coupled spin and elastic waves are calculated with the change in the ratio between the average value ε and rms fluctuation Δε of the coupling parameter between waves from the homogeneous case (ε ≠ 0, Δε = 0) to the extremely randomized case (ε = 0, Δε ≠ 0) at various correlation wavenumbers of inhomogeneities k_c. For the limiting case of infinite correlation radius (k_c = 0), in addition to approximate expressions, exact analytical expressions corresponding to the summation of all diagrams of elements of the matrix Green’s function are obtained. The results calculated for an arbitrary k_c value in the new self-consistent approximation are compared to the results obtained in the standard self-consistent approximation, where only the first term of the expansion of the vertex function is taken into account. It is shown that the new approximation corrects disadvantages of the Green’s functions calculated in the standard approximation such as the dome shape of resonances and bends on the sides of resonance peaks. The appearance of a fine structure of the spectrum in the form of a narrow resonance on the Green’s function of spin waves and a narrow antiresonance on the Green’s function of elastic waves, which was previously predicted in the standard self-consistent approximation, is confirmed. With an increase in the parameter k_c, the Green’s functions calculated in the standard and new approximations approach each other and almost coincide with each other at k_c/k ≥ 0.5. At the same time, the results of this work indicate that the new self-consistent approximation has a certain advantage for studying the problems of stochastic radiophysics in media with long-wavelength inhomogeneities (small k_c values), because it describes both the shape and width of peaks much better than the standard approximation.

The magnetic and structural properties of a series of nonstoichiometric Ni–Mn–Ga Heusler alloys are theoretically investigated in terms of the density functional theory. Nonstoichiometry is formed in the coherent potential approximation. Concentration dependences of the equilibrium lattice parameter, the bulk modulus, and the total magnetic moment are obtained and projected onto the ternary phase diagram of the alloys. The stable crystalline structures and the magnetic configurations of the austenitic phase are determined.

We have analyzed the spectrum of gapless excitations emerging upon the perturbation of the Abrikosov lattice with a single flux quantum in the unit cell. Superconductors with Ginzburg–Landau parameter κ close to unity are of special interest. We have determined the spectrum of gapless excitations close to zeroth shear modes for an arbitrary angle ϕ between the unit cell vectors. Analysis of the excitation spectra of triangular and square lattices with a single flux quantum in the unit cell has shown that solutions with a number of flux quanta greater than one exist at least in the range of parameters κ close to unity (κ > 1) and give smaller values of the free energy as compared to its values for a triangular lattice with a single flux quantum. For small values of momentum k (in the k² approximation), the excitation spectrum of the “transverse” mode in the triangular lattice is independent of the direction of the momentum lying in the plane perpendicular to the magnetic field. For the square lattice (ϕ = π/2), the transverse mode is anisotropic in the k² approximation also.

The dielectric tensor of a low-dimensional metal system has been introduced on the basis of the density matrix in the relaxation time approximation. The properties of this tensor have been analyzed. It has been proved that anisotropy and nonlocality are decisive features of the response of low-dimensional systems to an electromagnetic field. In particular, the expression has been derived for the dielectric tensor of nanometer- thick metal films. It has been shown that the dielectric tensor components can be reduced to the Drude dielectric function for a homogeneous metal in the case when the film thickness considerably exceeds the effective electron mean free path. The application of the classical distribution function for describing electrons in the film is justified under these conditions.

The structural inhomogeneity of a lipid bilayer is an obstacle to applying the classical Canham–Helfrich model to describe its dynamics on nanometer length scales. In this paper, a refined expression for the free energy of a single-component lipid bilayer is used to describe the dynamics of lipid density fluctuations. In particular, the expression with a term involving the gradient of the area per lipid [8] is used for the free energy per lipid. A refined expression has been derived for the dynamic structure factor of a free lipid bilayer in the hydrodynamic region. It leads to differences in the interpretation and values of the bilayer parameters in comparison with the standard model.