Transparent Semiconductor-Superconductor Interface and Induced Gap in an Epitaxial Heterostructure Josephson Junction

TL;DR

This study uses multiple Andreev reflection measurements to demonstrate a highly transparent semiconductor-superconductor interface in an epitaxial heterostructure Josephson junction, revealing an induced gap close to the superconductor's gap.

Contribution

It provides direct quantification of interface transparency and characterizes the induced superconducting gap in an epitaxial InAs/Al heterostructure Josephson junction.

Findings

Near-unity transmission at the interface.

Induced gap of approximately 180 μeV.

Subband structure revealed by carrier density dependence.

Abstract

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.