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Temperature dependences of the basal-plane electrical resistance of underdoped YBa 2 Cu 3 O t − δ single crystals are investigated in a broad temperature range down to the superconducting transition, after a fast cooldown from 650 ° C as well as after a room-temperature annealing. A stepped behavior of the superconducting transition has been observed, pointing to an inhomogeneity of the samples. Annealing has been revealed to lead to a narrowing of the superconducting transition and a reduction of both, the residual resistivity and the phonon scattering coefficient. This is accompanied by a slight increase of the Debye temperature attributed to a decrease of the lattice parameter caused, in turn, by a redistribution of the labile oxygen. The revealed changes of the parameters of the temperature dependence of the electrical resistance point to an equalization of the concentration of the labile oxygen in the layers and its ordering. [ABSTRACT FROM AUTHOR]

Abstract: The electrical resistance in the range of Т C–300K in the layer planes of YВа2Сu3О7−δ single crystals with a range of oxygen deficiency (providing a range of T C from 78 to 92K) was investigated. The experimental data is approximated by an expression that accounts for the scattering of electrons on phonons, as well as on defects and the fluctuation conductivity in a 3-D model of the Aslamazov-Larkin theory. According to this approximation, depending upon the oxygen deficiency, the Debye temperature varies from 245 to 400K, coherence length ξ С(0)≈0.5Å. [Copyright &y& Elsevier]

Abstract: In the present work the effect of hydrostatic pressure up to 10kbar on in-plane electrical resistivity of well-structured YBa2Cu3O7−δ (δ<0.15, Т с≈91K, ΔТ с≈0.3K) single crystals was investigated. The influence of the twin boundaries on the electrical resistivity was minimized. The resistivities temperature dependences in the interval Т с up to 300K can be approximated by taking into account the linear term at high temperatures and the fluctuation conductivity (Maki–Thompson model) near Т с. The parameters of the linear dependence of R(T) are decreasing as the pressure is increasing. Т с increases linearly when the pressure increases with the derivative dT c /dP≈0.080K/kbar. Among the Maki–Thompson model parameters the inter-layer distance, d, can be considered to be independent from pressure, the transverse coherence length, ξ c (0)∼0.1d. [Copyright &y& Elsevier]

Abstract: We investigate the relaxation of the normal electrical resistivity, induced by high-pressure in YBa2Cu3O6.45 single crystals. It is determined that the pressure affects to the phase composition of the sample. Under pressure phases with different (but similar) critical temperatures form. It is determined that the application-removal pressure process is completely reversible. Above T c the temperature dependence of the resistivity in the layers'' plane at different hydrostatic pressures can be approximated with high accuracy with the scattering of electrons by phonons model. With increasing pressure, the residual resistance is reduced and the contribution of intraband s–s scattering increases. Additionally, the role of the interband s–d scattering and the Debye temperature is enhanced. [Copyright &y& Elsevier]

Abstract: We have investigated the conductivity in the basis plane of YBaCuO single crystals slightly doped by Al and Pr with a pre-specified topology of twin boundaries. The excess conductivity for the analyzed samples shows dependence in a wide temperature range , where is the mean field temperature of superconducting transition. The temperature dependence of the pseudogap can be satisfactorily described in terms of the BCS–BEC crossover theoretical model. [Copyright &y& Elsevier]

The influence of hydrostatic pressure P up to 1.05 GPa on resistivity ρ , excess conductivity σ ′ ( T ) and pseudogap Δ ⁎ ( T ) is investigated in slightly doped single crystals of YBa 2 Cu 3 O 7− δ ( T c ( P = 0 ) ≈ 49.2 K and δ ≈ 0.5 ). The critical temperature T c is found to increase with increasing pressure at a rate dT c / dP =+ 5.1 KGPa − 1 , while ρ ( 300 K ) decreases at a rate d ln ρ / dP = ( − 19 ± 0.2 ) % GPa − 1 . Near T c , independently on pressure, σ ′ ( T ) is well described by the Aslamasov–Larkin and Hikami–Larkin fluctuation theories, demonstrating a 3D–2D crossover with increase of temperature. The crossover temperature T 0 determines the coherence length along the c -axis ξ c ( 0 ) ≃ ( 3.43 ± 0.01 ) A ˚ at P =0, which is found to decrease with increasing P . At the same time, Δ ⁎ and the BCS ratio 2 Δ ⁎ / k B T c both increase with increasing hydrostatic pressure at a rate d ln Δ ⁎ / dP ≈ 0.36 GPa − 1 , implying an increase of the coupling strength with increasing P . At low temperatures below T pair , the shape of the Δ ⁎ ( T ) curve is found to be almost independent of pressure. At high temperatures, the shape of the Δ ⁎ ( T ) curve changes noticeably with increasing P , suggesting a strong influence of pressure on the lattice dynamics. This unusual behavior is observed for the first time. [ABSTRACT FROM AUTHOR]