Critical and Gaussian Conductivity Fluctuations in Granular Ho1−x Pr x Ba2Cu3O7−δ Superconductor

摘要

Fluctuations in the electrical conductivity of polycrystalline Ho1−x Pr x Ba2Cu3O7−δ superconductors were investigated with Ho contents from x=0.01 up to 0.10. Samples were prepared by the standard solid-state reaction technique. The method of analysis is based on the determination of the quantity $chi_{sigma}^{-1}=-frac{d}{dT}lnDeltasigma$ , where Δσ=σ−σ R is the fluctuation conductivity. The results show that the resistive transition proceeds in two stages as seen by the temperature derivative of the resistivity near T C . In the normal phase, Gaussian and critical fluctuation conductivity regimes were identified. The pairing transition splitting, associated with Pr doping and related to the occurrence of a phase separation, as observed in studies with other rare earth elements, was not clearly observed. On approaching the zero-resistance state, our results show a power-law behavior that corresponds to a phase transition from a paracoherent to a coherent state of the granular array. This behavior was not affected by Pr doping.