Effective activation energy U(J,H) in epitaxial YBa2Cu3O7−δ thin films

Abstract

We have measured the resistivity of epitaxial YBa2Cu3O7−δ thin film as a function of temperature, current density and the magnetic field up to 8 T. The current density dependence of the effective activation energy exhibits a slight increase in the low current density range below 103 A/cm2 and a logarithmic decline in higher current density with increasing current density. The magnetic field dependence of the effective activation energy showed a crossover of vortex state from a quasi-2D for H//ab-plane to a 3D line liquid state for H//c-axis. The possible dissipation mechanisms responsible for the ln H dependence of the effective activation energy were discussed.