DEPENDENCE OF THE VORTEX-SOLID PHASE-TRANSITION OF YBA2CU3O7-DELTA THIN-FILMS ON ANISOTROPY - EVIDENCE FOR A UNIVERSAL PHASE-BOUNDARY

The vortex-solid phase boundary of YBa2Cu3O7-delta (YBCO) thin films w as studied as a function of oxygen stoichiometry, delta, using magneto transport measurements. Experimental evidence for a characteristic cro ssover field, H-0, separating two distinct types of behavior, was obse rved for films with delta>0.12 to occur at a temperature, T-0, that is about half of the superconducting transition temperature (T-0 approxi mate to T-c/2). When plotted as H-g(T)/H-0 versus (1-T/T-c), all of th e boundaries collapse onto a single universal curve. An implication of this collapse is that an empirical equation which depends only on T-c , the anisotropy gamma, and T-0, H-g(T) = H-0[(1 - T/T-c)/(1 - T-0/T-c )](n), where H-0 = [1.2 phi(0)/(sy)(2)], can be used to describe the H -g(T) boundary for any YBCO thin film and other disordered YBCO materi als. Estimates of the vortex-glass (VG) correlation length, xi(VG), ar e made. The value of xi(VG) at the point where VG scaling finally brea ks down is found to be independent of magnetic field for the fully oxy genated films, however, it is dependent on field for deoxygenated film s. This result suggests that the pinning in the fully oxygenated films is dominated by correlated disorder while pinning in the deoxygenated films becomes dominated by quenched disorder.