PHASE-TRANSITION FROM SOLID TO LIQUID-PHASE OF VORTEX LATTICE IN YBA2CU3O7 THIN-FILMS

We measured voltage V versus current I curves with a function of temperature T and magnetic field H for YBa2Cu3O7 single-crystalline thin films. The characteristics of the pinning type was found to be changed with the change in T, in contradiction to Kramer's scaling law. Furthermore, we analyzed I-V curves in terms of the flux creep model proposed by Anderson and Kim. In low H region the product of flux bundle volume vd and its jump distance l decreased with the increase of H, while in high H region the product increased rapidly with H, suggesting a rapid increased of interaction length between vortices. These results imply all evidence of an occurence of vortex liquid phase in the high H regime. We showed that the transition region between the above two regimes is located in the vicinity of H at which the critical current density begins to decrease rapidly with the increase of H. © 1990.