FLUCTUATION CONDUCTIVITY OF POLYCRYSTALLINE YbBa2Cu3O7 -δ SUPERCONDUCTORS

Abstract

We have studied the effect of superconducting fluctuations on the electrical conductivity of granular samples of YbBa 2 Cu 3 O 7 -δ superconductors. Two different polycrystalline samples were prepared for this study. Special attention is taken above T c , where Gaussian and critical regimes are observed. Far from T c , we can observe the regime dominated by Gaussian fluctuations, with exponent approximately [Formula: see text], which is the predicted one for homogeneous 3D fluctuations. Inside the critical region, we have observed two power-law regimes: one of them is consistent with predictions for the 3D-XY universality class, with exponent [Formula: see text]. Below T c , in the approach to the zero resistance state, our results show a power-law behavior with critical exponents s1 = 2.6 ± 0.2 and s2 = 4.2 ± 0.3. We have previously shown that this corresponds to a phase transition from a paracoherent to a coherent state of the granular array.