DEPENDENCE OF CRITICAL-CURRENT DENSITY ON OXYGEN EXPOSURE IN NB-ALOX-NB TUNNEL-JUNCTIONS

We demonstrate that a large fraction of the available data relating th e critical current density J(c) of superconducting Nb-AlOx-Nb tunnel j unctions to oxidation parameters can be accounted for by a single, nea rly universal dependence, For fixed oxidation temperature, J(c) does n ot depend independently on oxygen partial pressure and oxidation time, but only on their product. There are two distinct regimes in this dep endence, corresponding to high and low J(c).