Surface Nucleation and Boundary Conditions in Superconductors

We have calculated the surface nucleation field as a function of the slope of the superconducting order parameter at the surface of a semi-infinite superconducting half-space. When the order parameter increases on approaching the surface, as would be the case in the presence of a surface region of enhanced transition temperature, nucleation fields larger than those expected for a uniform sample are predicted. Cold working the surface on an InBi foil produces this condition and qualitatively confirms the prediction.