  The combination of strong spin-orbit coupling, large $g$-factors, and the
coupling to a superconductor can be used to create a topologically protected
state in a semiconductor nanowire. Here we report on growth and
characterization of hybrid epitaxial InAsSb/Al nanowires, with varying
composition and crystal structure. We find the strongest spin-orbit interaction
at intermediate compositions in zincblende InAs$_{1-x}$Sb$_{x}$ nanowires,
exceeding that of both InAs and InSb materials, confirming recent theoretical
studies \cite{winkler2016topological}. We show that the epitaxial InAsSb/Al
interfaces allows for a hard induced superconducting gap and 2$e$ transport in
Coulomb charging experiments, similar to experiments on InAs/Al and InSb/Al
materials, and find measurements consistent with topological phase transitions
at low magnetic fields due to large effective $g$-factors. Finally we present a
method to grow pure wurtzite InAsSb nanowires which are predicted to exhibit
even stronger spin-orbit coupling than the zincblende structure.
