Critical exponents of conductivity fluctuations in high-temperature superconductors

Abstract

The critical exponents of conductivity fluctuation spectra of high-temperature superdonductors have been calculated. A dynamic scaling model of critical superconducting fluctuations is presented to account for the observed temperature dependence. In this approach, the problem of the distribution of random conductivities is mapped into the problem of diffusion in the presence of random potential barriers, which is relevant to the disordered structure of these materials. The predictions of the model are consistent with recent conductivity fluctuation measurements on three different samples of YBa₂Cu₃O_7-δ. The power-law dependence of the spectrum on the temperature, particularly near the critical temperature, is indicative of a phase transition associated with the existence of percolation granular networks in the matrix of the cuprate compounds.