Effect of Barium Codoping on Superconductivity in SrxBi2Se3

JETP Letters - A structural reason for superconductivity in a Cu-, Sr-, or Nb-atom-doped Bi2Se3 topological insulator is still unclear. To understand this reason, a codoping approach has been...     

Vicinal Growth as a Possible Structural Source of the Nematic Superconductivity in Sr x Bi 2 Se 3

The structure of the layered SrxBi2Se3 crystals characterized by the nematic superconductivity has been studied. It is shown that the higher the degree of the superconducting and structural nematicity, the stronger the deviation of the block boundary orientation from the crystal c axis. This indicates that the block grows at an angle to the basal planes, rather than along them. This growth can result in the formation of the preferred direction in a system.     

Anomalous effect of magnetic field on the low-temperature thermal expansion of the Bi2Sr2?xLaxCuO6+δ and Nd2?xCexCuO4?δ HTSC systems in the non-superconducting phase

The thermal expansion of single crystals of the Bi₂Sr_2−x La _x CuO_6+δ high-temperature superconducting (HTSC) system in the insulating phase with compositions having no superconducting transition to a temperature of 1.8 K (x ≥ 0.8) is measured in an arbitrary direction in the (ab) plane in the temperature range of 7–50 K. Temperature regions of material compression upon heating are found. The study of anomalies in magnetic fields of 3 and 6 T, parallel and perpendicular to the c-axis revealed an anisotropic and nonmonotonic effect of the field on thermal expansion. Such anomalies for the n-type Nd_2−x Ce _x CuO_4−δ HTSC sample also having no superconducting transition are detected for the first time. The results show that the anomaly nature is caused by anisotropic electronic ordering, probably, by the charge density wave in the CuO₂ plane and superconductivity fluctuations in the insulating phase.     

X-ray diffraction analysis of quantum-size ZnMgSSe/ZnSe/ZnMgSSe nanostructures

Quantum-size ZnMgSSe/ZnSe/ZnMgSSe nanostructures were studied by X-ray diffraction analysis. It was found that the ZnMgSSe solid solution decomposes into two phases with close lattice parameters. As the lattice-parameter mismatch between zinc selenide and barrier layers increases, the decomposition is accompanied by simultaneous broadening of peaks of each phase. It was found that almost pure ZnSe grows in the first stages of metastable barrier layer growth, thus thickening the well (ZnSe).     

Propagation of nonequilibrium acoustic phonons in high-purity coarse-grained ZnTe

Propagation of nonequilibrium acoustic phonons in coarse-grained ZnTe obtained through vacuum sublimation was studied using the heat pulse method under both optical and metallic-heater phonon generation. The phonon mean free paths in the samples studied were shown to be 14 µm and to be dominated by scattering from twin boundaries.     

Ablation of (111) and (001) Crystal Plates by Ultrashort Laser Pulses with Rotated Linear Polarization

JETP Letters - The dependence of the threshold fluence for surface ablation of such crystalline materials as silicon and diamond (with orientations (001) and (111)) on the direction of linear...     

Comprehensive study of structural and optical properties of LT-GaAs epitaxial structures

The results of the comprehensive study of LT-GaAs epitaxial structures on GaAs and Si substrates by high-energy electron diffraction, reflection anisotropy spectroscopy, atomic force microscopy, X-ray diffraction, Raman scattering, and photoluminescence methods are presented. The results obtained indicate the existence of several channels of nonequilibrium carrier recombination, which depend, in particular, on the substrate type and on the complex dependence of the concentration of structural imperfections on the used technology and growth conditions of the structures.     

Unconventional Low-Temperature Luminescence Kinetics in Micro- and Nanopowders of the Anatase Phase of Titanium Dioxide

JETP Letters - It is shown that the low-temperature (5 K) decay kinetics of the known luminescence band of titanium dioxide (anatase) in the range of 2.0–2.5 eV has a power-law character. For...     

Nonequilibrium acoustic phonons in ZnTe at liquid-helium temperatures: Effect of impurities and structural defects on the phonon mean free path

ZnTe crystallites isolated from a druse of coarse-grained polycrystalline ZnTe, prepared by chemical vapor synthesis at a temperature of ～650°C, were studied using x-ray diffractometry, luminescence, and the heat pulse technique. The crystallites are stacked in {110}-oriented macroscopic layers with a common twin system. The {111} twin planes separated at a distance of 50–100 μm are perpendicular to the (110) growth layers. Acoustic phonon propagation was studied using the heat pulse technique. A comparison of the responses to the arrival of differently polarized phonons in a given sample with the responses obtained on high-purity coarse-grained ZnTe with randomly distributed twin systems with a separation of 5–10 μm and on twin-free single-crystal ZnTe suggests that twins radically affect the scattering of acoustic phonons. The mean free paths of LA, FTA, and STA phonons were determined by comparing the experimental responses with Monte Carlo calculations.