Excess conductivity in the paracoherence regime of pure and Ag doped (La1−xY x)2Ba2CaCu5Oz superconductors

The temperature variations of electrical resistivity have been measured on pure and 5 wt% Ag doped (La1−xY x)2Ba2CaCu5Oz superconductors in the absence and presence of 1 T magnetic field. The resistivity data were analyzed in terms of excess conductivity due to phase fluctuations of the order parameter in the paracoherence regime. In zero field case, we observed ordered phase fluctuations with the critical exponent mostly comparable to that of 3D XY ferromagnet and a crossover to disordered phase fluctuations with critical exponent comparable to that of diluted Heisenberg ferromagnet at higher temperatures. In the presence of a magnetic field, only ordered phase fluctuations have been observed.