FLUCTUATION OF THE MAGNETOCONDUCTIVITY IN POLYCRYSTALLINE Y_0.95Tb_0.05Ba₂Cu₃O_7-δ SUPERCONDUCTORS

Abstract

The electrical magnetoconductivity near the superconducting transition in granular samples of Y 0.95 Tb 0.05 Ba 2 Cu 3 O 7-δ was experimentally studied. The measurements were performed using low magnetic fields up to 50 Oe, applied parallel to the current. Results showed that the transition proceeds in two stages as seen by the temperature derivative of the resistivity near TC. The analysis of the conductivity in the normal phase has evidenced contributions from Gaussian and critical fluctuations. In the regime of near zero resistance state, the occurrence of a coherence transition was evidenced, which was related to the connective nature of the granular samples. We have obtained the field independent exponents λC = 4.6 ± 1.1 and λC ≅ 6.7 ± 0.7 for fluctuation conductivity in the coherence transition.