Investigation of structural features of the Y3Al5O12: Ce3+/Lu2O3 crystal phosphors formed by the colloidal chemical method

The specific features of the crystal structure of crystal phosphors Y₃Al₅O₁₂: Ce³⁺/Lu₂O₃ (Lu₂O₃: Ce) synthesized by the colloidal chemical method have been investigated by neutron diffraction at room temperature. The influence of the method used for introducing Lu₂O₃ into the system on the structure and luminescence properties of the samples has been analyzed. The investigation has revealed that the spectra of the samples prepared under the most nonequilibrium conditions are characterized by the Stokes shift and high photoluminescence intensity. This has been explained by the disorder of their crystal structure due to the formation of stable associates of defects.     

The modified absorption optic method for diagnostics of the wave liquid film on a rotating surface

The modification of absorption optic method for diagnostics of the wave liquid film on the surface of a rotating disk was proposed. Inaccuracy of the method was estimated analytically and experimentally. The field measurements of liquid film thickness on a rotating disk were carried out.     

Collective volume plasmons in manganites with nanoscale phase separation: simulation of the measured infrared spectra of La(0.7)Ca(0.3)MnO3

Optical characteristics of manganites with nanoscale electronic phase separation are simulated using an exact renormalization group transformation in Kirchhoff's equations. The local electric field is found to be highly inhomogeneous, exceeding the incident-wave field by orders of magnitude when the permittivities of the phases have opposite signs and plasmons are excited. The spatial scale of the field fluctuations suggests the collective character of the plasmon modes. The results of the simulation explain the optical anomalies of La(0.7)Ca(0.3)MnO(3) single crystals and films in the infrared frequency range in a natural way.     

Optical measurement of instantaneous liquid film thickness based on total internal reflection

An optical method of measuring the instantaneous transparent liquid film thickness, based on the effect of total internal reflection by the gas-liquid interface, is represented. A light circle whose diameter is proportional to the liquid film thickness and eccentricity is proportional to the slope gradient of the liquid film surface in the measurement region is formed around a small-size light source in the plane of vessel bottom. Using several light sources, the method allows measurement of the liquid film thickness field. The method is implemented in a multichannel meter of transparent liquid film thickness and curvature surface, with computer image processing.     

Surface barrier and magnetic hysteresis of ac permeability in YBaCuO single crystal

The nature of hysteretic behavior of the flux line lattice (FLL) contribution to ac magnetic permeability (μ_v) is analyzed for the case of YBa₂Cu₃O_x single crystal (at applied magnetic field Hc axis). It is shown that hysteresis loops μ_v(H) corresponding to different temperatures (T=70–84 K) are scaled to a universal curve in normalized coordinates. Such a behavior is interpreted in terms of the FLL interaction with the crystal surface. The explicit relationship between μ_v and magnetic induction B is found for the near-surface region of the superconductor. It is shown that the μ_v(H) loops are closely related to the hysteresis of B at cycling of applied magnetic field. The latter hysteresis stems from the Bean–Livingston surface barrier. The estimates demonstrate strong suppression of the surface barrier in YBa₂Cu₃O_x crystal in comparison to that expected for the ideal surface. As a result, the lower branch of the hysteresis loop corresponding to the increasing field is very close to the equilibrium μ_v(H) curve and the surface barrier appreciably affects only the upper branch when magnetic flux leaves the sample. The comparison of theoretical predictions and experimental data provides an opportunity to refine the actual range of stability H_max(B)–H_min(B) for the FLL at fixed B for YBa₂Cu₃O_x crystal in the case of Hc.     

Inhomogeneous electron states in the systems with imperfect nesting

A brief overview of the theoretical studies on the electronic phase separation in the systems with the imperfect nesting of Fermi surface sheets is presented. Among these systems, there are chromium and its alloys, superconducting iron-based pnictides, bilayer graphene, and some other materials.     

Effect of direct current on higher harmonic generation in the frequency spectrum of magnetoimpedance of amorphous wires with circular anisotropy

The effect of direct current on the nonlinear response of magnetoimpedance in circularly anisotropic amorphous wires is investigated. A model is proposed for calculating the voltage across the ends of the wire in the case of a weak skin effect in the sample. It is shown that a direct current passing through the wire can substantially increase the amplitude of even harmonics of the voltage. The conditions in which the sensitivity of the second harmonic to the applied magnetic field is maximal are determined.     

The stationary sine-Gordon equation on metric graphs: Exact analytical solutions for simple topologies

We consider the stationary sine-Gordon equation on metric graphs with simple topologies. Exact analytical solutions are obtained for different vertex boundary conditions. It is shown that the method can be extended for tree and other simple graph topologies. Applications of the obtained results to branched planar Josephson junctions and Josephson junctions with tricrystal boundaries are discussed.     

Nonuniform self-organized dynamical states in superconductors with periodic pinning

We consider magnetic flux moving in superconductors with periodic pinning arrays. We show that sample heating by moving vortices produces negative differential resistivity (NDR) of both N and S type (i.e., N- and S-shaped) in the voltage-current characteristic (VI curve). The uniform flux flow state is unstable in the NDR region of the VI curve. Domain structures appear during the NDR part of the VI curve of an N type, while a filamentary instability is observed for the NDR of an S type. The simultaneous existence of the NDR of both types gives rise to the appearance of striking self-organized (both stationary and nonstationary) two-dimensional dynamical structures.     

Phase transition in a vortice lattice in a Bi2212:Pb single crystal

The magnetooptical method was used to investigate the penetration of a magnetic flux into a single crystal of a high-temperature superconductor (Bi_0.84Pb_0.16)_2.2Sr₂CaCu₂O₈ in crossed magnetic fields. It is shown that at low temperatures the penetration of the magnetic flux is anisotropic: the flux moves preferentially along the magnetic field applied in the plane of the sample, and the anisotropy grows as the temperature increases. At a temperature T_m = 54±2 K, there occurs a sharp change in the character of penetration of the magnetic field into the superconductor; the direction of the flux ceases be dependent on the direction and magnitude of the magnetic field applied in the plane of the sample. In this case, the transition temperature T_m is independent of the applied magnetic field. The effect is interpreted in terms of the concepts of a phase transition in the system of vortices, which is related to a sharp decrease in the correlations in the position of vortices in various CuO planes, i.e., with the transition from three-dimensional to two-dimensional behavior of the vortex structure.