Proximity effect and interface transparency in Al/InAs-nanowire/Al diffusive junctions

Abstract

We investigate the proximity effect in InAs nanowire (NW) junctions with superconducting contacts made of Al. The carrier density in InAs is tuned by means of the back gate voltage Vg. At high positive Vg the devices feature transport signatures characteristic of diffusive junctions with highly transparent interfaces - sizable excess current, re-entrant resistance effect and proximity gap values (ΔN) close to the Al gap (Δ0). At decreasing Vg, we observe a reduction of the proximity gap down to ΔN ≈ Δ0/2 at NW conductances ∼2 e2 h-1, which is interpreted in terms of carrier density dependent reduction of the Al/InAs interface transparency. We demonstrate that the experimental behavior of ΔN is closely reproduced by a model with rectangular potential barrier at the Al/InAs interface.