Surface pinning as origin of high critical current in YBa₂Cu₃Ox thin films

We give theoretical and experimental evidence that high critical currents in laser ablated YBa2Cu3Ox films can be due to the pinning of vortices by surface roughness. The theory, which takes into account the bending of the vortex core and its orthogonality to the film surface, predicts that any surface elevation causes an increase in the core length and therefore produces an energy barrier whose height is proportional to the film thickness and can exceed bulk pinning barriers. Comparison with experiments gives satisfactory agreement with the value of critical current density and shows that the latter can be explained by the pinning at a steplike surface relief.