  Low-temperature magnetotransport measurements are performed on GaAs/InSb
core-shell nanowires. The nanowires were self-catalyzed grown by molecular beam
epitaxy. The conductance measurements as a function of back-gate voltage show
an ambipolar behavior comprising an insulating range in between the transition
from the p-type to the n-type region. Simulations based on a self-consistent
Schr\"odinger--Poisson solver revealed that the ambipolar characteristics
originate from a Fermi level dependent occupation of hole and electron states
within the approximately circular quantum well formed in the InSb shell. By
applying a perpendicular magnetic field with respect to the nanowire axis,
conductance fluctuations were observed, which are used to extract the
phase-coherence length. By averaging the magneto-conductance traces at
different back-gate voltages, weak antilocalization features are resolved.
Regular flux-periodic conductance oscillations are measured when an axial
magnetic field is applied. These oscillations are attributed to closed-loop
quantized states located in the InSb shell which shift their energetic position
periodically with the magnetic flux. Possible reasons for experimentally
observed variations in the oscillation patterns are discussed using simulation
results.
