EFFECT OF OXYGEN STOICHIOMETRY ON THE VORTEX-GLASS PHASE-TRANSITION IN YBA2CU3O7-DELTA THIN-FILMS

A series of YBa2Cu3O7-delta epitaxial thin films were prepared with va lues of delta ranging from 0.05 to 0.65. Electric field as a function of current-density isotherms could be scaled to a universal scaling fu nction over the full delta range and the critical parameters determine d were nearly independent of delta. The vortex-glass phase-transition temperature was determined as a function of magnetic field at all of t he values of delta studied and the phase boundary was observed to broa den with delta. Based on determinations of the ratio of the zero-tempe rature coherence length xi(c0) to c-axis lattice parameter using norma l-state fluctuation conductivity, the anisotropy was shown to increase with delta while xi(c0) decreases from 1.6 to 0.8 angstrom as delta r anges from 0.05 to 0.37.