Effect of surface and bulk pinning on the distribution of transport current in superconducting film

We show, both experimentally and theoretically, that the inhomogeneous distribution of transport current produced by two contacts located at the opposite corners of a square film changes significantly as the film becomes superconducting. We analyze two possible sources for such a re-distribution: (1) the nonlinear dependence of the resistivity on the current density and (2) the effect of surface barriers. In the above geometry these sources have the opposite effect and compete with each other. This technique can be easily modified for various sample/contact geometries and is useful for the analysis of surface and bulk pinning of vortices