Spin-mixing enhanced proximity effect in aluminum-based superconductor-semiconductor hybrids

TL;DR

This paper demonstrates that adding heavy adatoms like platinum to aluminum enhances its magnetic field resilience, enabling robust superconductor-semiconductor hybrids suitable for topological qubits in high magnetic fields.

Contribution

It introduces a method to increase aluminum's critical magnetic field using heavy adatoms, improving its suitability for high-field quantum applications.

Findings

Al/Pt films increase aluminum critical field by over two times.

Superconductivity in InSb nanowires persists up to 7T with Al/Pt.

Two-electron charging remains robust with heavy adatoms.

Abstract

In superconducting quantum circuits, aluminum is one of the most widely used materials. It is currently also the superconductor of choice for the development of topological qubits. In this application, however, aluminum-based devices suffer from poor magnetic field compatibility. In this article, we resolve this limitation by showing that adatoms of heavy elements (e.g. platinum) increase the critical field of thin aluminum films by more than a factor of two. Using tunnel junctions, we show that the increased field resilience originates from spin-orbit scattering introduced by Pt. We exploit this property in the context of the superconducting proximity effect in semiconductor-superconductor hybrids, where we show that InSb nanowires strongly coupled to Al/Pt films can maintain superconductivity up to 7T. The two-electron charging effect, a fundamental requirement for topological quantum computation, is shown to be robust against the presence of heavy adatoms. Additionally, we use non-local spectroscopy in a three-terminal geometry to probe the bulk of hybrid devices, showing that it remains free of sub-gap states. Finally, we demonstrate that semiconductor states which are proximitized by Al/Pt films maintain their ability to Zeeman-split in an applied magnetic field. Combined with the chemical stability and well-known fabrication routes of aluminum, Al/Pt emerges as the natural successor to Al-based systems and is a compelling alternative to other superconductors, whenever high-field resilience is required.