S. G. Chernook

Quantum oscillations in heavily doped bismuth chalcogenides

The observation of Shubnikov-de Haas and Hall oscillations in high-quality Bi2 − xCuxSe3 single crystals is reported. Measurements carried out upon rotating the samples with respect to the magnetic field demonstrate that the oscillations originate from two-dimensional surface states in three-dimensional single crystals and are determined only by the perpendicular component of the magnetic field.

Growth and structure of superconducting FeSe crystals

Superconducting crystals of iron selenide FeSe are grown and their phase and elemental compositions are studied. The structural analysis of individual FeSe1 − x crystals showed the coexistence of two phases in this compound. The resistivities and magnetic susceptibilities of the crystals are investigated.

Vapor-phase growth of Bi2Sr2Can−1CunOx (n= 1–3) single crystals

High-quality platelike Bi2Sr2Can−1CunOx (n= 1–3) single crystals with superconducting transition temperatures Tc=10, 85, and 110 K, respectively, are prepared by vapor-phase growth in closed cavities produced in a melt fluxed with KCl. The effect of synthesis and growth conditions on the Tc of the crystals is analyzed. The morphology of the crystals suggests that the most perfect, well-faceted crystals grow via vapor transport with constant feeding from the charge.

Growth, structure, and some transport properties of topological insulators based on bismuth chalcogenide single crystals

Single crystals of topological insulators—bismuth chalcogenides Bi2Te3, Bi2 − xSnxTe3, Bi2Se3, and Bi2 − xCuxSe3 with different charge-carrier densities—are grown by the modified Bridgman method. Their composition and structure are investigated and temperature dependences of the electric resistance and magnetic field dependences of the Hall voltage are obtained.

Structure and superconductivity of layered oxycarbonate Bi2Sr4Cu2CO3O8 crystals

A complex study of the elemental composition, structure, and superconducting properties of single crystals of layered oxycarbonate Bi2Sr4Cu2CO3O8 has been performed taking into consideration the growth and postgrowth annealing conditions.

Properties of fluorosilicate glass prepared by MCVD

Multilayer and two-layer fiber preforms with a fluorosilicate glass core have been produced by the modified chemical vapor deposition (MCVD) process with SiF4 as a fluorination agent. The fluorine profile across the preforms has been studied, the fluorine concentration in the glass has been determined as a function of the initial vapor mixture composition, and the effect of the fluorine concentration on the refractive-index difference between the fluorosilicate and silica glasses and on the mechanical stress in the glass has been examined. Comparison of the present results with literature data demonstrates that the above parameters depend significantly on the fluorosilicate glass preparation process: MCVD or plasma chemical vapor deposition (PCVD). This is tentatively attributed to the difference in structure between the glasses made by MCVD and PCVD.

Growth and properties of layered oxycarbonate Bi2Sr4Cu2CO3O8 single crystals

Layered oxycarbonate Bi2Sr4Cu2CO3O8 single crystals have been obtained for the first time by free growth in closed vapor-phase cavities. The morphology, structure, composition, and superconducting properties of these crystals have been investigated.

Dependence of superconducting properties of underdoped Bi-2201 single crystals on the charge composition and growth conditions in gas-filled cavities

High-quality Bi2 + xSr2 − yCuO6 + δ (Bi-2201) single crystals with the ratio Bi/Sr = 1.4–2.0 were grown by the free growth method in gas-filled cavities in KCl solution-melt in a range of doping levels, which provides variation in superconducting properties from insulators to optimally doped crystals. The charge composition Bi : Sr : Cu = 1.7 : 2.3 : 2.5 with excess Sr and Cu and synthesis conditions provided growth cavity formation in the KCl solution at the crystal growth stage. Lamellar single crystals and whiskers were grown under quasi-equilibrium conditions of lowered growth temperatures and partial oxygen pressure, achieved in closed gas-filled cavities.

Growth from gas cavities in a molten salt and properties of superconducting Bi2Sr2CaCu2O8+δ single crystals

Perfect single crystals of the high-temperature superconductor Bi2Sr2CaCu2O8+δ with the superconducting transition temperature TC = 72–85 K (depending on the crystallization conditions) are obtained by the method of free growth in gas cavities formed in a KCl solution-melt. The specific features of the growth process are in the formation of an enclosed growth gas cavity in a (previously synthesized) blend of a specified phase composition dissolved in KCl and the free crystal growth in this cavity. The combination of growth and high-temperature annealing in the same process made it possible to obtain uniform (ΔTC = 1.5 K) single crystals with stable superconducting properties. Annealing of the grown single crystals in oxygen or in air in the temperature range 400–850°C confirmed that the crystals with maximum values of TC are optimally doped.

Two-band superconductivity of Sn 1– x In x Te crystals with T c = 3.6–3.8 K

The Andreev reflection spectra of high-quality superconducting Sn1–xInxTe crystals with critical temperature Tc = 3.6–3.8 K were examined. The two-band nature of the superconducting state of this compound was established. The energy gaps have s-symmetry and were measured to be 2Δ1/kTc = 3.5 ± 0.9 and 2Δ2/kTc = 7 ± 1. Neither of the contacts with a resistance of 1.5–23 Ω revealed a peak at zero voltage typical of the topological superconducting state.