Depairing currents in superconducting films of Nb and amorphous MoGe

We report on measuring the depairing current J(dp) in thin superconducting films as a function of temperature. The main difficulties in such measurements are that heating has to be avoided, either due to contacts, or to vortex flow. The latter is almost unavoidable since the sample cross section is usually larger than the superconducting coherence length xi(s) and the magnetic field penetration depth lambda(s). On the other hand, vortex flow is helpful since it homogenizes the distribution of the current across the sample. We used a pulsed current method, which allows us to overcome the difficulties caused by dissipation and measured the depairing current in films of thin polycrystalline Nb (low lambda(s), low specific resistance rho) and amorphous Mo0.7Ge0.3 (high lambda(s), high rho), structured in the shape of bridges of various width. The experimental values of J(dp) for different bridge dimensions are compared with theoretical predictions by Kupriyanov and Lukichev for dirty limit superconductors. For the smallest samples we find a very good agreement with theory, over essentially the whole temperature interval below the superconducting critical temperature.