Phase equilibria and growth of β-BaB2O4 crystals in the BaB2O4-Ba2Na3[B3O6]2F system

A complex investigation of the BaB₂O₄-Ba₂Na₃[B₃O₆]₂F cut, which belongs to the ternary mutual Ba, Na//BO₂, F (BaB₂O₄-(NaBO₂)₂-(NaF)₂-BaF2) system, has been performed. The cut is quasibinary, with the following eutectics coordinates: 810 ± 5°C, 85 mol % Ba₂Na₃[B₃O₆]₂F, 15 mol % BaB₂O₄. It is shown that this system can be used to grow bulk β-BaB₂O₄ crystals.     

Down-Conversion of Short-Wavelength Radiation in LBO Crystal

Russian Physics Journal - Comparative model analysis of the possibilities of down-conversion into the terahertz (THz) frequency range of radiation of all-solid-state femtosecond Ti:Sapphire laser...     

Surface spin-polarized currents generated in topological insulators by circularly polarized synchrotron radiation and their photoelectron spectroscopy indication

A new method for generating spin-polarized currents in topological insulators has been proposed and investigated. The method is associated with the spin-dependent asymmetry of the generation of holes at the Fermi level for branches of topological surface states with the opposite spin orientation under the circularly polarized synchrotron radiation. The result of the generation of holes is the formation of compensating spin-polarized currents, the value of which is determined by the concentration of the generated holes and depends on the specific features of the electronic and spin structures of the system. The indicator of the formed spin-polarized current can be a shift of the Fermi edge in the photoelectron spectra upon photoexcitation by synchrotron radiation with the opposite circular polarization. The topological insulators with different stoichiometric compositions (Bi_1.5Sb_0.5Te_1.8Se_1.2 and PbBi₂Se₂Te₂) have been investigated. It has been found that there is a correlation in the shifts and generated spin-polarized currents with the specific features of the electronic spin structure. Investigations of the graphene/Pt(111) system have demonstrated the possibility of using this method for other systems with a spin-polarized electronic structure.     

Specific features of the electronic,spin, and atomic structures of a topological insulator Bi<Subscript>2</Subscript>Te<Subscript>2.4</Subscript>Se<Subscript>0.6</Subscript>

The specific features of the electronic and spin structures of a triple topological insulator Bi₂Te_2.4Se_0.6, which is characterized by high-efficiency thermoelectric properties, have been studied with the use of angular- and spin-resolved photoelectron spectroscopy and compared with theoretical calculations in the framework of the density functional theory. It has been shown that the Fermi level for Bi₂Te_2.4Se_0.6 falls outside the band gap and traverses the topological surface state (the Dirac cone). Theoretical calculations of the electronic structure of the surface have demonstrated that the character of distribution of Se atoms on the Te–Se sublattice practically does not influence the dispersion of the surface topological electronic state. The spin structure of this state is characterized by helical spin polarization. Analysis of the Bi₂Te_2.4Se_0.6 surface by scanning tunnel microscopy has revealed atomic smoothness of the surface of a sample cleaved in an ultrahigh vacuum, with a lattice constant of ~4.23 Å. Stability of the Dirac cone of the Bi₂Te_2.4Se_0.6 compound to deposition of a Pt monolayer on the surface is shown.     

Electronic polarization effects in the photodissociation of Cl2

Velocity mapped ion imaging and resonantly enhanced multiphoton ionization time-of-flight methods have been used to investigate the photodissociation dynamics of the diatomic molecule Cl(2) following excitation to the first UV absorption band. The experimental results presented here are compared with high level time dependent wavepacket calculations performed on a set of ab initio potential energy curves [D. B. Kokh, A. B. Alekseyev, and R. J. Buenker, J. Chem. Phys. 120, 11549 (2004)]. The theoretical calculations provide the first determination of all dynamical information regarding the dissociation of a system of this complexity, including angular momentum polarization. Both low rank K = 1, 2 and high rank K = 3 electronic polarization are predicted to be important for dissociation into both asymptotic product channels and, in general, good agreement is found between the recent theory and the measurements made here, which include the first experimental determination of high rank K = 3 orientation.     

New nonlinear optical crystals of the M1 ? xSc3 ? yYx + y(BO3)4 (M = Ce, Pr, or Nd) family

New Y_0.57M_0.72Sc_2.71(BO₃)₄ (M = Pr or Nd) nonlinear optical crystals of the huntite structural type with sp. gr. R32 were grown by the high-temperature solution-melt method. The analogous phase with cerium was prepared by solid-state synthesis. Lattice parameters were established by X-ray diffraction patterns of the powder.     

Crystallization of AgGaS2 melts enriched with Ag2S and Ga2S3

In this work we consider experiments with directed crystallization of melts with slight deviation from stoichiometric composition of AgGaS₂. The evolution of melt composition was calculated for both experiments using measured chemical composition of the solid phase. Also the difference in unit cell parameters and luminescence spectra for AgGaS₂ grown from the melts was found. Both monocrystal samples and samples synthesized from elementary Ag, Ga and S were used for thermal analyses. Obtained data suggests that different ways of preparing the samples are responsible for defects concentration and thus for so wide range (70°C) of melting temperatures reported in scientific literature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties and electronic structure of BiTeCl and BiTeBr compounds

Optical properties of BiTeCl and BiTeBr compounds with a strong Rashba spin–orbit coupling are studied in the 0.08–5.0 eV range using the optical ellipsometry method. Fundamental characteristics of the electronic structure are obtained. Similarly to BiTeI, spectra of the imaginary part of dielectric permittivity constant ε₂(E) in the energy interval between the plasma edge and the threshold of an intense interband absorption (0.7 eV in BiTeCl and 0.6 eV in BiTeBr) display a fine structure of electronic transitions at 0.25 and 0.55 eV in BiTeCl and 0.20 and 0.50 eV in BiTeBr. These features are assigned to electronic transitions between the bulk conduction zones split by the Rashba spin–orbit interaction. The parameters of the electronic structure of BiTeCl and BiTeBr are compared with the BiTeI compound that was studied earlier. In the BiTeCl–BiTeBr–BiTeI row, the absorption edge and main features of the fundamental absorption exhibit a shift to low energies.     

Charge dissolution and heat and mass transfer during hydrothermal crystal growth with heat field rotation

Crystallography Reports - Analytical modeling of laminar thermal gravitational convection in a vertical porous cylinder of radius R and height H (R is much smaller than H) with a low-compressed...