Vortex-glass transition and Jc( H, T) characteristics in epitaxial YBa 2Cu 3O 7− δ thin films

Abstract

We have measured the isothermal current–voltage ( I– V) curves as a function of temperature T and magnetic field H up to 10 T in the case of applied magnetic field parallel and perpendicular to the c-axis in an epitaxial YBa 2Cu 3O 7− δ thin film. The I– V curves for a fixed magnetic field can be well scaled by vortex-glass (VG) theory, indicating the VG transition in the film. We find the evidence that the dependence of critical current density J c on magnetic field and temperature is concerned in the VG transition. Below the VG line, J c follows an exponential-type field dependence, J c∝exp[− H/ H 0( T)]. Meanwhile, there is an abrupt change of J c above the VG line. The temperature dependence of the critical current density above the VG line follows an exponential law, J c= J c0exp(− T/ T 0). These imply that there exists distinguishable mechanisms of flux pinning above and below the VG line.