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 values 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 function over the full delta range and the critical parameters determined were nearly independent of delta. The vortex-glass phase-transition temperature was determined as a function of magnetic field at all of the values of delta studied and the phase boundary was observed to broaden with delta. Based on determinations of the ratio of the zero-temperature coherence length xi(c0) to c-axis lattice parameter using normal-state fluctuation conductivity, the anisotropy was shown to increase with delta while xi(c0) decreases from 1.6 to 0.8 angstrom as delta ranges from 0.05 to 0.37.