Gate-tunable proximity effect in epitaxial Al-InAs Josephson junctions using hBN gate dielectric*

The transparent interface of epitaxial Al-InAs heterostructures provides an excellent platform for potential advances in topological superconductivity and superconducting quantum computation. Josephson junctions built on these heterostructures can be gated, allowing for tuning of the supercurrent. We report the fabrication and measurement of gate-tunable Al-InAs Josephson junctions in which the gate dielectric in contact with the InAs was mechanically exfoliated hexagonal boron nitride (hBN). We discuss fabrication processes that enable compatibility between layered material transfer and Al-InAs heterostructures. By comparing these devices with others using a conventional AlOx gate dielectric, we show that hBN is a suitable gate dielectric for the Al-InAs material platform. Specifically, the product of normal resistance and critical current, is comparable for both types of devices, but higher R_N for the hBN-based devices suggests the possibility of less unintentional doping of the InAs by the gate dielectric.