Effect of small oxygen deficiency on the para-coherent transition and 2D–3D crossover in untwinned YBa2СuзО7−δ single crystals

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]