Superconductivity and Parity Preservation in As-Grown In Islands on InAs Nanowires

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-centered 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.