HALL CONDUCTIVITY FLUCTUATIONS IN EPITAXIAL YBa2Cu3O7-δ THIN FILMS

Abstract

We present systematic measurements of the longitudinal and Hall resistivities in YBa2Cu3O7-δ epitaxial thin films. Above the critical temperature, T c , the longitudinal resistivity, ρxx(T), increases linearly with temperature, whereas the Hall resistivity, ρxy(T), varies inversely proportional to T. Consequently, the cotangent of the Hall angle shows quadratic temperature dependence. The fluctuation contributions to both the longitudinal and Hall conductivities in the normal phase are studied. In the case of the longitudinal conductivity, 2D and 3D Gaussian regimes are observed. In addition, a genuine 3D-XY critical regime is discerned closely above T c in experiments performed at low applied fields. The value of the corresponding critical exponent, λ C =0.33, indicates that the dynamic universality class for the superconducting transition in the analyzed system is given by the Model E of Hohenberg and Halperin. The analysis of the Hall conductivity fluctuations above T c reveals the occurrence of 2D and 3D Gaussian regimes which are consistent with those identified in the longitudinal conductivity results. Below T c the Hall resistivity shows a sign reversal before attaining the zero resistance state.