FLUCTUATION-INDUCED CONDUCTIVITY OF POLYCRYSTALLINE Er1-xTbxBa2Cu3O7-δ SUPERCONDUCTORS

Abstract

We have studied fluctuations on the electrical conductivity of granular compounds of Er 1-x Tb x Ba 2 Cu 3 O 7-δ(0 ≤ x ≤ 0.10) superconductors. From the temperature derivative of the resistivity, we have found that the transition proceeds in two intragranular–intergranular stages, with intergranular character accentuated for higher concentrations of terbium (x ≅ 0.10). The data also revealed the occurrence of critical regimes, as well as fluctuation regimes beyond 3D-XY. However, for higher concentrations of terbium, it was not possible to observe fluctuation regimes beyond 3D-XY, probably because TbBa 2 Cu 3 O 7-δ is a metastable phase. Below TC, on approaching the zero resistance state, our results showed a power-law behavior with critical exponents consistent with a phase transition from a paracoherent to a coherent state of the granular array.