Non-Ohmic Conductivity, Fluctuations and Dimensional Crossover in YBaCuO

Abstract

We report a non-Ohmic excess conductivity measured in an YBa2Cu3O7-x single crystal in the absence of an applied magnetic field. Mean-field paraconductivity data are in agreement with a recent theory (1992) of a clean layered superconductor in an electric field. In a strong enough electric field, a continuous dimensional crossover from three-dimensional to two-dimensional (2D) behaviour takes place at the superconducting transition point. A broadening of the temperature dependence of the resistive transition is attributed to large 2D out-of-plane non-linear fluctuations.