  Understanding the spatial distribution of charge carriers in III-V nanowires
proximity coupled to superconductors is important for the design and
interpretation of experiments based on hybrid quantum devices. In this letter,
the gate-dependent surface accumulation layer of InAsSb/Al nanowires was
studied by means of Andreev interference in a parallel magnetic field. Both
uniform hybrid nanowires and devices featuring a short Josephson junction
fabricated by shadow lithography, exhibited periodic modulation of the
switching current. The period corresponds to a flux quantum through the
nanowire diameter and is consistent with Andreev bound states occupying a
cylindrical surface accumulation layer. The spatial distribution was tunable by
a gate potential as expected from electrostatic models.
