Proximity Effect Transfer from NbTi into a Semiconductor Heterostructure via Epitaxial Aluminum

We demonstrate the transfer of the superconducting properties of NbTi—a large-gap high-critical-field superconductor—into an InAs heterostructure via a thin intermediate layer of epitaxial Al. Two device geometries, a Josephson junction and a gate-defined quantum point contact, are used to characterize interface transparency and the two-step proximity effect. In the Josephson junction, multiple Andreev reflection reveal near-unity transparency, with an induced gap ${\mathrm{\Delta }}^{\ast }=0.50\mathrm{m}\mathrm{e}\mathrm{V}$ and a critical temperature of $7.8\mathrm{K}$. Tunneling spectroscopy yields a hard induced gap in the InAs adjacent to the superconductor of ${\mathrm{\Delta }}^{\ast }=0.43\mathrm{m}\mathrm{e}\mathrm{V}$ with substructure characteristic of both Al and NbTi.