Vortex dynamics in superconducting films: Comensurability and surface effects

The penetration and further evolution of stiff vortex lines in a supercondu cting film under a parallel magnetic field is numerically simulated. A squa re array of in-plane columnar defects is considered as a periodic pinning p otential. It is shown that the strong surface effects play an important rol e in the commensurability between the vortex lattice and the pinning potent ial. The matching peaks of the magnetization curve are associated to a stab le composite vortex lattice in which two distinc vortex lattices are commen surate with the pinning potential.