  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.
