Superconducting Proximity Effect in InAsSb Surface Quantum Wells with In Situ Al Contacts

We demonstrate robust superconducting proximity effect in InAs$_0.5$Sb$_0.5$ quantum wells grown with epitaxial Al contact, which has important implications for mesoscopic and topological superconductivity. Unlike more commonly studied InAs and InSb semiconductors, bulk InAs$_0.5$Sb$_0.5$ supports stronger spin-orbit coupling and larger $g$-factor. However, these potentially desirable properties have not been previously measured in epitaxial heterostructures with superconductors, which could serve as a platform for fault-tolerant topological quantum computing. Through structural and transport characterization we observe high-quality interfaces and strong spin-orbit coupling. We fabricate Josephson junctions based on InAs$_0.5$Sb$_0.5$ quantum wells and observe strong proximity effect. These junctions exhibit product of normal resistance and critical current, $I_cR_N = \SI{270}{\micro V}$, and excess current, $I_exR_N = \SI{200}{\micro V}$ at contact separations of 500~nm. Both of these quantities demonstrate a robust and long-range proximity effect with highly-transparent contacts.