Vortex dynamics at the transition to the normal state in YBa 2Cu 3O 7- δ films

We propose a description of the vortex dynamics in YBa₂Cu₃O_7-δ films from the critical to the normal states. This description supposes that the vortex motion is thermally activated along the twin boundaries of the films. The discontinuity observed in the current-voltage curves at the transition to the normal state is explained by the sudden increase in the dissipated power rate due to vortex depinning. However, near the critical temperature, this phenomenon does not occur because the vortex activation energy is near zero. We also show how the current at the transition to the normal state can be computed from the current-voltage curves measured at low currents. The predictions of this description are compared to the data published by [M.T. González, J. Viña, S.R. Currás, J.A. Veira, J. Maza, F. Vidal, Phys. Rev. B 68 (2003) 054514].