ANISOTROPIC PROPERTIES OF THE FLUCTUATIONAL CONDUCTIVITY IN YBCO

We report on resistive transitions in YBCO films as a function of stre ngth and orientation of the applied magnetic field. Angular behaviour is found to be markedly different in the upper and lower part of the t ransition. At high dissipation level, an angular scaling behaviour is observed, following the anisotropic Lawrence-Doniach expression for th e upper critical field. The scaling breaks down at the midpoint of the transition. No scaling is observed at lower temperatures, even if dif ferent angular scaling functions are used. The results are very well i nterpreted in terms of superconducting fluctuations above rho/rho(n)=0 .5 and pinning phenomena below.