title: Proximity Effect Transfer from NbTi into a Semiconductor Heterostructure via Epitaxial Aluminum.
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 reflections reveal near-unity transparency with an induced gap Δ* = 0.50 meV and a critical temperature of 7.8 K. Tunneling spectroscopy yields a hard induced gap in the InAs adjacent to the superconductor of Δ* = 0.43 meV with substructure characteristic of both Al and NbTi.
authors.affiliation: Center for Quantum Devices and Station Q Copenhagen, Niels Bohr Institute University of Copenhagen , Universitetsparken 5, 2100 Copenhagen, Denmark.
authors.forename: A C C
authors.initials: AC
authors.lastname: Drachmann
authors.affiliation: Center for Quantum Devices and Station Q Copenhagen, Niels Bohr Institute University of Copenhagen , Universitetsparken 5, 2100 Copenhagen, Denmark.
authors.forename: H J
authors.initials: HJ
authors.lastname: Suominen
authors.affiliation: Center for Quantum Devices and Station Q Copenhagen, Niels Bohr Institute University of Copenhagen , Universitetsparken 5, 2100 Copenhagen, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Kjaergaard
authors.forename: B
authors.initials: B
authors.lastname: Shojaei
authors.forename: C J
authors.initials: CJ
authors.lastname: Palmstrøm
authors.affiliation: Center for Quantum Devices and Station Q Copenhagen, Niels Bohr Institute University of Copenhagen , Universitetsparken 5, 2100 Copenhagen, Denmark.
authors.forename: C M
authors.initials: CM
authors.lastname: Marcus
authors.affiliation: Center for Quantum Devices and Station Q Copenhagen, Niels Bohr Institute University of Copenhagen , Universitetsparken 5, 2100 Copenhagen, Denmark.
authors.forename: F
authors.identifier: 0000-0002-6320-5754
authors.initials: F
authors.lastname: Nichele
keywords: Superconductivity; epitaxial aluminum; indium arsenide; niobium titanium; proximity effect; two-dimensional electron gas