Fluctuation-induced conductivity of polycrystalline Gd1-xCexBa2Cu3O7-δ superconductor

This paper reports on measurements of the resistive transition in polycrystalline Gd1-xCexBa2Cu3O7-δ samples (x = 0.000, 0.025 and 0.050). The samples were produced by a standard solid state reaction method and in two different thermal routes. The microstructure was analyzed by X-ray diffraction. The samples were considered homogeneous since no extra peaks due to impurity phase were observed. To identify power-law divergences in conductivity, the results were analyzed in terms of the temperature derivative of the resistivity and the logarithmic temperature derivative of the conductivity (d ln (Δσ) =dT). From the results, the occurrence of a two-stage transition besides the pairing transition splitting for sample with x = 0.050 was observed. Such splitting was associated with Ce doping and related with the occurrence of a phase separation. In the normal phase, Gaussian and critical fluctuations conductivity regimes were identified. On approaching the zero resistance state, our results showed a power-law behavior that corresponds to a phase transition from a paracoherent to a coherent state of the granular array.