Fluctuation-induced conductivity of polycrystalline (Ho-Ce)Ba2Cu3O7-δ superconductor

We report on systematic conductivity fluctuation measurements on samples of Ho1-xCexBa2Cu3O7-δ with x = 0.00, 0.05, and 0.10. The samples were produced by a standard solid-state reaction method, and the microstructure was analyzed by X-ray diffraction. To identify power-law divergences of the conductivity, the results were analyzed in terms of the temperature derivative of the resistivity dp/dT and with the logarithmic derivative of the conductivity with respect to temperature -d ln(Δσ)/dT. It was observed that the critical temperature decreases and that the transition width increases with increasing Ce doping. The data showed the occurrence of a two-stage transition besides the pairing transition splitting, associated with Ce doping and related with the occurrence of a phase separation. Above the critical temperature, the Gaussian and critical regimes were observed. 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. (author)