Effect of Long Aging on the Resistivity Properties of Aluminum Doped YBa2Cu3−y Al y O7−δ Single Crystals with a Given Twin Boundary Topology

We investigate the conducting properties in the basal ab-plane before and after a long time exposure in air atmosphere of aluminum doped YBa2Cu3−y Al y O7−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 (T c ) can be adequately described within the Aslamazov-Larkin theoretical model. Nevertheless, the description of the excess conductivity through the relation Δσ∼(1−T/T∗)exp(Δ∗ab/T), can be interpreted in terms of the mean-field theory, where T ∗ is the mean field temperature of the superconducting transition and the temperature dependence of the pseudo-gap is satisfactorily described by the BEC-BCS crossover theory. It is determined that the prolonged exposure increases significantly the temperature range of the implementation of the pseudogap state, thus narrowing the linear section of the resistivity dependence ρ ab (T).