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

A. V. Bubis, A. O. Denisov, S. U. Piatrusha, I. E. Batov, J. Becker, J. Treu, D. Ruhstorfer, G. Koblmüller, V. S. Khrapai

Published 2017-05-01Version 1

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 $V_g$. At high positive $V_g$ the devices feature transport signatures characteristic of diffusive junctions with highly transparent interfaces - sizable excess current, re-entrant resistance effect and proximity gap values ($\Delta_N$) close to the Al gap ($\Delta_0$). At decreasing $V_g$, we observe a reduction of the proximity gap down to $\Delta_N\approx\Delta_0/2$ at NW conductances $\sim2e^2/h$, which is interpreted in terms of carrier density dependent reduction of the Al/InAs interface transparency. We demonstrate that the experimental behavior of $\Delta_N$ is closely reproduced by a model with shallow potential barrier at the Al/InAs interface.