Andreev bound states in hybrid full-shell Al/InAs nanowire devices

Hybrid superconductor-semiconductor nanowire (NW) devices have attracted widespread interest as they can host Majorana zero modes (MZMs). While most of the previous experiments dealt with semiconductor NWs partially covered by a superconductor, a recent theory proposal [1] suggests to fully cover the semiconductor NWs with a superconductor. One of the main advantages of having a superconducting full-shell is that MZMs should arise at a very precise magnetic field, namely in the odd lobes of the Little-Parks effect. A first result [2] showed the presence of a zero bias peak (ZBP) in the first lobe, suggesting the presence of MZMs in such NWs. However, also Andreev bound states (ABS) could arise in such experiments. Hence, it is important to study them and especially their evolution in a magnetic field. Here, we present low temperature magnetotransport data using InAs NWs fully covered by Al [3]. We investigate ABS in the Little-Parks regime; we show that ABS can merge at zero bias in the first lobe, mimicking MZMs behaviour. Furthermore, we suggest how to discriminate ZBPs arising from MZMs and from ABS.

[1] R. M. Lutchyn et al. arXiv:1809.05512 (2018).
[2] S. Vaitiekenas et al. arXiv:1809.05513 (2018).
[3] P. Krogstrup et al., Nature Materials 14, 400 (2015).