EXCESS CONDUCTIVITY IN THE MEAN FIELD AND PARACOHERENCE REGIMES OF (La1.6Y0.4)Ba2Ca0.8Cu4.8Oz SUPERCONDUCTORS

Abstract

The temperature variations of electrical resistivity have been measured on pure and 5 wt% Ag doped ( La 1.6 Y 0.4) Ba 2 Ca 0.8 Cu 4.8 O z superconductors. These data were analyzed in terms of fluctuation-induced excess conductivity in the mean field regime by using the Aslamazov–Larkin (AL), Lawrence–Doniach (LD) and Maki–Thompson (MT) models. The fluctuations in the amplitude of order parameter are found to be two dimensional in nature in the mean field region. The estimated values of the average phase breaking time τϕ (100 K) are found to be 3.9×10-16 s and 4.6×10-16 s for pure and Ag doped samples respectively. The resistivity data were also analyzed in terms of excess conductivity due to phase fluctuations of the order parameter in the paracoherence region. The critical exponent is found to be mostly comparable to that of the 3D XY ferromagnet in the vicinity of zero resistivity temperature and the diluted Heisenberg model at a higher temperature.