RESISTIVE TRANSITION IN THE YBA2CU3O7 SYSTEM EVIDENCE OF 2D-3D DIMENSIONAL CROSSOVER

We have carried out detailed resistive measurements in the superconducting region of the twinned and untwined YBa2Cu3O7-y (YBCO) crystals. The data show that there exists two resistive anomalies in the transition regime. A distinct resistive ''shoulder'' at rho(s)/rho(n) almost-equal-to 20 % in field is observed in all the samples and persists to 16 T. An additional resistive ''kink'' at rho(k)/rho(n) almost-equal-to 10 % exists in a range of external magnetic fields. The results strongly suggest that the lower resistive kink is related to the vortex lattice melting transition. Depending on the sample, presumably related to the pinning strength, the transition is either a liquid or a glassy-like state. On the other hand, the upper resistive knee is associated with the 2D-3D crossover of the superconducting transition.