Measurement of multiple Andreev reflection (MAR) in a Josephson junction made from an InAs heterostructure with epitaxial aluminum is used to quantify the highly transparent semiconductor-superconductor interface, indicating near-unity transmission. The observed temperature dependence of MAR does not follow a conventional BCS form, but instead agrees with a model in which the density of states in the quantum well acquires an effective induced gap, in our case 180 {\mu}eV, close to that of the epitaxial superconductor. Carrier density dependence of MAR is investigated using a depletion gate, revealing the subband structure of the semiconductor quantum well, consistent with magnetotransport experiment of the bare InAs performed on the same wafer.
@article{arxiv.1607.04164,
title = {Transparent Semiconductor-Superconductor Interface and Induced Gap in an Epitaxial Heterostructure Josephson Junction},
author = {M. Kjaergaard and H. J. Suominen and M. P. Nowak and A. R. Akhmerov and J. Shabani and C. J. Palmstrøm and F. Nichele and C. M. Marcus},
journal= {arXiv preprint arXiv:1607.04164},
year = {2017}
}