  We report electron transport studies on InSb-Al hybrid
semiconductor-superconductor nanowire devices. Tunnelling spectroscopy is used
to measure the evolution of subgap states while varying magnetic field and
voltages applied to various nearby gates. At magnetic fields between 0.7 and
0.9 T, the differential conductance contains large zero bias peaks (ZBPs) whose
height reaches values on the order 2e2/h. We investigate these ZBPs for large
ranges of gate voltages in different devices. We discuss possible
interpretations in terms of disorder-induced subgap states, Andreev bound
states and Majorana zero modes.
