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We reveal that the temperature dependence of the basal-plane normal-state electrical resistance of optimally doped YBa 2 Cu 3 O 7 − δ single crystals can be with great accuracy approximated within the framework of the model of s-d electron-phonon scattering. This requires taking into account the fluctuation conductivity whose contribution exponentially increases with decreasing temperature and decreases with an increase of oxygen deficiency. Room-temperature annealing improves the sample and, thus, increases the superconducting transition temperature. The temperature of the 2D-3D crossover decreases during annealing. [ABSTRACT FROM AUTHOR]

Abstract: The electrical resistivity in the ab-plane of the Y1−y Pr y Ва2Сu3О7−δ single crystals with high degree of perfection in the interval of Т c – 300K was investigated. The increasing of praseodymium content leads to the reduction of the critical temperature (T c ) from 92 to 30K. The experimental results can be approximated by the expression, taking into account the scattering of electrons by phonons, defects, the fluctuation conductivity in the 3D Aslamazov–Larkin model, as well as the transition to a “semiconductor” type behavior of the resistivity at the high praseodymium concentrations. The concentration dependences of all fitting parameters indicate a structural transition in the region 0.35≤у≤0.43. In particular, the Debye temperature changes in this range from 350 to 550K, and the transverse coherence length passes through a maximum ξ С (0)≈5Å. The concentration dependence of the critical temperature testifies the d-pairing of the BCS model. [Copyright &y& Elsevier]

Abstract: We investigate the conducting properties in the basal ab-plane before and after a long time exposure in air atmosphere of the optimally oxygen doped YBa2Cu3O7−δ single crystals. Prolonged exposure leads to an increase of the effective scattering centers of the normal carriers. The excess conductivity in a wide temperature range has exponential temperature dependence and near the critical temperature is well described within the Aslamazov–Larkin theoretical model. The prolonged exposure increases to a great extent the temperature range of the implementation of the pseudogap state, narrowing the linear section of the temperature dependence of the resistivity in the ab-plane, ρ ab(Т). [Copyright &y& Elsevier]

Abstract: We investigate the influence of the disorientation angle between the direction of a constant magnetic field (up to 15kOe) and the ab-plane α ≡∠(H,ab) to the temperature dependence of the excess conductivity in the temperature interval of the transition to the superconducting state in untwinned YBa2Cu3O7−δ single crystals. We discuss the appearance of low temperature “tails” (para-coherent transitions) on the resistive transitions, corresponding to different phase regimes of the vortex-matter state. At temperatures above the critical temperature, the temperature dependence of the excess para-conductivity is interpreted within the Hikami–Larkin theoretical model of the fluctuation conductivity for layered superconductors. [Copyright &y& Elsevier]

Abstract: The temperature dependence of the transport anisotropy of ReBa2Cu3O7−δ (Re=Y, Ho) single crystals is investigated. We experimentally determine the parallel and perpendicular conductivity in oxygen deficient single crystals. It is found that, in these single crystals, oxygen deficiency results to uneven oxygen distribution within their volume that leads to the formation of superconducting phases with different critical temperatures. We present an analysis regarding the agreement of the experimental data with the predictions of different theoretical models. It is determined that, the absolute values of the energy gaps along and perpendicular to the basis plane are changed, with different signs of their derivatives. When the value of Δ c increases, the value of the pseudo-gap decreases and vice versa, testifying that the PG regime is suppressed, with a synchronous strengthening of the localization effects. In distinction to YBa2Cu3O7−δ , the temperature dependence of the anisotropy of the resistivity ρ c /ρ ab (T) for the HoBa2Cu3O7−δ samples is well described, by the universal “law of 1/2” for the thermally activated hopping conductivity. [Copyright &y& Elsevier]

Abstract: The influence of hydrostatic pressure of up to 11kbar on the fluctuation conductivity in the ab plane of the YBa2Cu3O7−δ (YBCO) single crystals with various oxygen concentrations is studied. In contrast to samples of stoichiometric composition, the application of high pressure on samples with oxygen deficiency, leads to the decrease of the coherence length perpendicular to the ab plane ξ c(0). The pressure-induced redistribution of the labile oxygen causes a shift of the temperature interval in which three-dimensional superconducting fluctuations exist and a diffusion redistribution of the labile components from the phase of lower critical temperature to the high-temperature superconducting phase. [Copyright &y& Elsevier]

Studies the effect of hydrostatic pressure on pressure, temperature and time dependences of the conductivity in the ab-plane of single crystals with different oxygen concentrations. Parameters of single crystals with different superconducting transition temperature; Peculiarities in the behavior of dependences due to several mechanisms.

Investigates the effect of low-temperature annealing on the superconducting transition temperature and electrical resistance of single crystals of YBa(sub 2)Cu(sub 3)O(sub 7-sigma) quenched from temperatures of 620-650 degrees Celsius. Increase in transition temperature and decrease in resistance during annealing; Isothermal relaxation of resistance.

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 influence of praseodymium content on the basis plane conductivity of Y1− х Pr х Ba2Cu3O7− δ single crystals. An increase of the praseodymium concentration leads to the enhancement of the localization effects and the appearance of a metal–insulator transition in the system, which always precedes the superconducting transition. The increase of the concentration of praseodymium, leads to a significant displacement of the point of the metal–insulator transition in the low temperature region. [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]

Evolution of the excess conductivity in YBCO single crystals is investigated after their step-by-step irradiation with fast electrons. The dependence of the coherence length ξ c (0) along the c -axis on the irradiation dose dependence is obtained. It is revealed that an increase of the irradiation dose from 1.4 to 8.8 × 1018 cm − 2 leads to a considerable extension of the temperature range of the excess conductivity. This is accompanied by a factor of about 1.5 increase of ξ c (0) and a shift ot the 2D-3D crossover point in temperature. [ABSTRACT FROM AUTHOR]

• YBCO single crystals are irradiated with fast electrons and annealed in oxygen atmosphere. • The irradiation and annealing lead to a broadening of the superconducting transition. • Resistivity temperature dependence is described by a combination of different conductivity mechanisms. • Annealing allows one to recover the normal conducting properties to the initial, non-irradiated state. The effect of annealing on the conductivity of optimally doped YBa 2 Cu 3 O 7 − δ single crystals irradiated with fast electrons is investigated. The variation of width of the superconducting transition with increase of the irradiation dose and in the course of annealing is associated with the evolution of the sample inhomogeneity. A recovery of the critical temperature T c after annealing to some intermediate value between those in the initial and irradiated states is observed. This recovery of T c is accompanied by a substantial narrowing of the superconducting transition whose width nicely matches that in the non-irradiated state. The observed transition narrowing is attributed to an improvement of the sample homogeneity in consequence of the diffusion-induced growth and eventual coalescence of superconducting domains. In addition, the complete recovery of the normal conductivity after annealing points to a reversible change of parameters of the charge carriers scattering on phonons and defects. [ABSTRACT FROM AUTHOR]

Abstract: The system of equations that describes the temporal and spatial evolution of low-energy phonons (l-phonons) is obtained for the cases of plane and axial symmetry. From the solutions of these equations, we discuss the time-resolved measurements of the angular distribution of l-phonons. These show a rather unusual mesa shape with a flat top in the direction normal to the heater. We consider that the flat top is due to the creation of high-energy phonons (h-phonons). [Copyright &y& Elsevier]