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

TL;DR

This paper demonstrates the transfer of superconducting properties from NbTi into an InAs heterostructure through epitaxial aluminum, achieving high interface transparency and a hard induced gap, advancing superconductor-semiconductor hybrid devices.

Contribution

It introduces a novel two-step proximity effect transfer method using epitaxial aluminum to embed NbTi superconductivity into InAs heterostructures, with detailed characterization.

Findings

Near-unity interface transparency in Josephson junctions

Induced superconducting gap of 0.50 meV with a T_c of 7.8 K

Hard induced gap of 0.43 meV in InAs with characteristic substructure

Abstract

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 $\Delta^*=0.50~\mathrm{meV}$ and a critical temperature of $7.8~\mathrm{K}$. Tunneling spectroscopy yields a hard induced gap in the InAs adjacent to the superconductor of $\Delta^*=0.43~\mathrm{meV}$ with substructure characteristic of both Al and NbTi.