Superconductivity and parity preservation in as-grown In islands on InAs nanowires

TL;DR

This paper demonstrates the in-situ growth of indium islands on InAs nanowires, revealing their structural properties and superconducting behavior, which extends the operational parameters of semiconductor/superconductor hybrids beyond traditional aluminum-based systems.

Contribution

It introduces a novel method for synthesizing In islands on InAs nanowires with preserved charge parity and superconductivity, expanding the potential for hybrid device applications.

Findings

In islands exhibit tetragonal crystal structure and specific orientations.

Superconducting gap of ~0.45 meV observed in devices.

Charge parity is preserved at temperatures >1.2 K and magnetic fields ~0.7 T.

Abstract

We report in-situ synthesis of crystalline indium islands on InAs nanowires grown by molecular beam epitaxy. Structural analysis by transmission electron microscopy showed that In crystals grew in a tetragonal body-centred crystal structure within two families of orientations relative to wurtzite InAs. The crystalline islands had lengths < 500 nm and low-energy surfaces, suggesting that growth was driven mainly by surface energy minimization. Electrical transport through In/InAs devices exhibited Cooper pair charging, evidencing charge parity preservation and a pristine In/InAs interface, with an induced superconducting gap ~ 0.45 meV. Cooper pair charging persisted to temperatures > 1.2 K and magnetic fields ~ 0.7 T, demonstrating that In/InAs hybrids belong to an expanding class of semiconductor/superconductor hybrids operating over a wider parameter space than state-of-the-art Al-based hybrids. Engineering crystal morphology while isolating single islands using shadow epitaxy provides an interesting alternative to previous semiconductor/superconductor hybrid morphologies and device geometries.