Large zero bias peaks and dips in a four-terminal thin InAs-Al nanowire device

We report electron transport studies of a thin InAs-Al hybrid semiconductor-superconductor nanowire device using a four-terminal design. Compared to previous studies, thinner InAs nanowire (diameter less than 40 nm) is expected to reach fewer subband regime. The four-terminal device design excludes electrode contact resistance, an unknown value, which has inevitably affected previously reported device conductance. Using tunneling spectroscopy, we find large zero bias peaks (ZBPs) in differential conductance on the order of 2e2/h. At specific gate voltage settings, we find a magnetic-field-driven transition between a zero bias peak and a zero bias dip while the zero-bias conductance sticks close to 2e2/h. We discuss a topologically trivial interpretation involving disorder, smooth potential variation and quasi-Majorana zero modes.