Vladimir V. Gridin

Temperature dependent photoluminescence of the Sn‐implanted InSe

Measurements of temperature dependent photoluminescence (PL) of Sn‐implanted InSe were carried between 5 K and room temperature (RT). We observe two broad structures in the PL spectra: one in the vicinity of E1≊2.2 eV and another at E2≊1.8 eV. With a decrease of temperature the energy E1 (E2) increases (decreases) by about 35 meV with respect to the RT values. The relative intensity of the PL structures, R12, also shows considerable temperature dependence. We present empirical relations for the temperature dependence of E1 and E2. Except for the low temperature data the temperature dependence of the absolute changes in E1 and E2 was found to be in reasonable agreement with the usual band gap behavior: αT2/(T+β). This was compared with the available PL data of virgin InSe. The results are interpreted in terms of the appearance of deep impurity levels approximately 0.6 eV above the valence band edge.

Magnetoresistance and thermoelectric power in U2Ni2Sn

Abstract Low-temperature magnetoresistance ( MR ) and thermoelectric power ( S ) measurements are presented for antiferromagnetic U 2 Ni 2 Sn. Appreciable remanence in the MR behaviour is observed. S changes its sign at T N = 24 K from small positive values above T N to large negative values at 6 K where it shows a well resolved minimum.

Quasi-particle vs vortex motion dissipation in the mixed state of YBa2Cu3O7−δ using a Corbino disk sample geometry

Abstract The mixed state resistive tail of sintered YBa 2 Cu 3 O 7−δ is studied using a Corbino disk sample geometry. When the transport current passes radially from the rim of the disk sample to its center, a two component potential drop signal is detected below T c . This drop is due to (i) quasiparticles W q and (ii) vortex-core-motion related contribution W φ . When the contact pairs measuring the total drop W are placed radially, W q ( r ) and W φ ( r ) are found to follow markedly distinctive r -functional dependences. This provides a unique possibility to deconvolute the relative strengths of both contributions. The results obtained suggest that the mixed state dissipation of high- T c superconductors is strongly influenced by the quasiparticle excitations in contrast to the case of conventional low critical temperature materials.

Low-temperature transport properties of U2Rh2Sn and U2Fe2Sn

Magnetoresistivity measurements of polycrystalline U2Rh2Sn in an applied magnetic field of 8.29 T reveal a sharp minimum at the antiferromagnetic transition temperature TN≊20 K. The thermoelectric power of U2Rh2Sn exhibits negative values for temperatures T⪯24 K. At T≊4 K, a large decrease in resistivity with lowering of temperature is observed for polycrystalline U2Fe2Sn. This anomaly originates from the occurrence of free tin on the grain boundaries of the sample giving a decrease in resistivity as a result of superconductivity.

Estimation of effective electronic mass from Gaussian fluctuations of the magneto-thermopower of the polycrystalline Bi2Sr2CaCu2Oy

Reports on High-Tc cuprates show that the magneto-thermopower, ΔS(T, H) ≡ S(T, H) – S(T, 0), has, as a function of temperature, a curved-triangle shape asymmetric around Tc, where it reaches its magnetic-field dependent peak value, ΔS(Tc, H). Approximating the shape of ΔS(T, H) by the asymmetric linear triangle of the form: ΔS(T, H) ΔS(Tc, H) ± α ±(H)(Tc – T), with positive α−(H) and α+(H) defined for the temperatures T Tc, respectively, one observes that α+ (H) ≠ α-(H). We consider an average, ΔSav(T, H) and a fluctuation, ΔSfl(T, H), contributions to the total magneto-thermopower, ΔS(T, H), and analyze typical experimental data on 2212 BSCCO. Using the experimental results for α±(H), we estimate the effective electronic mass of our material, m*/me 8, which is in a good agreement with the reported data for 2212 BSCCO.

Influence of a non-uniform current density profile on quasiparticle excitations and thermally activated flux creep in YBa2Cu3O7−σ

A method, using a Corbino disk sample geometry, is described and applied to study of resistive tails of sintered

Nonequilibrium effects in the thermal conductivity of Bi-based high temperature superconductors

YBCO

Low-temperature magnetoresistance of CePt2Sn2

. When the transport current passes radially from the rim of the disk sample to its center, the two component potential drop signal is detected below

Debye temperature estimation from superconducting fluctuations in thermoelectric power and resistance of polycrystalline BiPbSrCaCuO

T_c

Probing of high Tc sample texturing with a potentiometric ring

, which is due to (i) quasiparticles