Critical current density and flux pinning in vortex liquid regime for YBa 2Cu 3O 7− δ epitaxial thin films

Abstract

The critical current density J c for epitaxial YBa 2Cu 3O 7− δ thin films as a function of applied magnetic field, temperature and angle between the magnetic field and the ab plane has been measured in detail. We observed an evidence for the dramatic change of the critical current density J c above and below the vortex–glass transition line. In the vortex solid state, the field dependence of J c follows an exponential dependence was argued to be from the intrinsic pinning in layered structural superconductors. But in the pinned vortex–liquid state, the J c decreases more rapidly with increasing magnetic field. It was suggested that the nonlinear temperature dependence of J c( T) near T c was from the vortex–liquid pinning. The temperature dependence of the critical current density exhibited an exponential law, J c∝exp(− T/ T 0), in the pinned vortex liquid regime.