Depairing currents in superconducting films of Nb and amorphous MoGe

Original · EN

We report on measuring the depairing current Jdp 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 ξₛ and the magnetic field penetration depth λₛ. 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 to overcome the difficulties caused by dissipation and measured the depairing current in films of thin polycrystalline Nb (low λₛ, low specific resistance ρ) and amorphous Mo₀.₇Ge₀.₃ (high λₛ, high ρ), structured in the shape of bridges of various width. The experimental values of Jdp 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.