Long- to Short-Junction Crossover and Field-Reentrant Critical Current in Al/Ag-nanowires/Al Josephson Junctions

We have probed the superconducting proximity effect through long high-quality monocrystalline Ag nanowires, by realizing Josephson junctions of different lengths, with different superconducting materials. Thanks to the high number of junctions probed, both the contact resistance and electron diffusion constant could be determined, enabling a comparison of the measured switching current to theoretical prediction, over the entire regime from short to long diffusive junctions. Although the length dependence of the switching current is as expected, the amplitude of the RNIc, product is smaller than predicted by theory. We also address the magnetic field dependence of the switching current. The quasi-Gaussian decay of the switching current with field expected in a long narrow junction is observed for all superconducting contacts we used except for aluminum. We present the striking nonmonotonous effect of field on the switching current of junctions with aluminum contacts when probed in a four-wire configuration and analyze it in terms of improved quasiparticle thermalization by a magnetic field.