Transparent Semiconductor-Superconductor Interface and Induced Gap in an   Epitaxial Heterostructure Josephson Junction
  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. 
M. Kjaergaard, H. J. Suominen, M. P. Nowak, A. R. Akhmerov, J.   Shabani, C. J. Palmstr{\o}m, F. Nichele, C. M. Marcus
cond-mat.mes-hall cond-mat.supr-con