We report asymmetric current-voltage characteristics in superconducting films in a parallel magnetic field. The critical current, ${\mathit{I}}_{\mathit{c}}$, is found to differ by as much as 30% for negative and positive currents, and beyond ${\mathit{I}}_{\mathit{c}}$, the magnitude of the voltage is also different for positive and negative currents, ‖V(+I)‖≠‖V(-I)‖. The critical current difference ‖${\mathit{I}}_{\mathit{c}+}$‖-‖${\mathit{I}}_{\mathit{c}\mathrm{-}}$‖ has complicated behavior, changing sign as temperature and magnetic field are varied. We propose a model based on the Bean-Livingston surface barrier and inhomogeneous bulk pinning that accounts for all observed behavior.

• Received 7 February 1994

DOI:https://doi.org/10.1103/PhysRevB.49.9244