Search

Abstract: The effect of annealing at room temperatures on the conductivity in the basis plane of oxygen deficient HoВа2Сu3О7− δ single crystals, tempered from a temperature of 650°C is investigated. We determine that during the annealing process an extension of the area of the linear dependence of the resistivity ρab (T) occurs. A shift downwards of the temperature interval corresponding to the metal-to-insulator transition and a considerable transformation of the form of the resistivity transfers to the superconducting state was observed. The absolute value of the temperature that the pseudo-gap regime commences is reduced by about 20K. The results are attributed to labile oxygen ordering without changing the concentration of oxygen in the sample. The estimation of the cluster sizes is characterized by the differences in oxygen content. We perform a comparative analysis between the experimental data with the predictions of the high temperature superconductivity cluster theory. [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: 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]

Measures the current-voltage characteristics (IVC) for YBaCuO single crystals in a magnetic field applied at 45 degrees twinning planes. Derivation of the current- and field dependencies of the pinning potential from the IVC curves; Indication of the obtained dependencies; Control of the flux creep in the range of strong magnetic fields.

Abstract: We investigate the conductivity in the basis plane of the non-stoichiometric ReBa2Cu3O7−δ (Re=Y, Ho) single crystals. The excess conductivity (Δσ) is described by in the wide temperature range T f < T < T*, where T* is the mean field temperature of the superconducting transition. We determined that the temperature dependence of the pseudogap (PG) is described in terms of the BCS–BEC crossover theoretical model. It is observed that a reduction in the oxygen content leads to the widening of the temperature interval, in which the PG region is realized, and to the narrowing of the area of the ρ(T) linear dependence in the ab-plane. [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]