Real Critical Current Density and Material Power Law of YBa2Cu3O7-d Epitaxial Thin Film

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 UJand the real critical current density Jc at different fields and temperatures. It is shown that Jc is completely different from the conventional critical current density JE, which is determined by the electronic-field criterion. Thus, the time-honoured electronic-field criterion is no longer reasonable for high-Tc superconductors. By further investigation of the results of Jc and UJ, 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.