Abstract

The current–voltage characteristics have been measured on aYBa₂Cu3O₇-δ epitaxial thin film. Using a material power law, we determine the temperature and field dependencies of the characteristic pinning potential U_Jand the real critical current density J_c at different fields and temperatures. It is shown that J_c is completely different from the conventional critical current density J_E, which is determined by the electronic-field criterion. Thus, the time-honoured electronic-field criterion is no longer reasonable for high-T_c superconductors. By further investigation of the results of J_c and U_J, we are able to present a physical picture of the transformation of the pinning potential well with increasing temperature and hence determine the transition point from vortex-glass phase to vortex-liquid phase.