Closing of the Induced Gap in a Hybrid Superconductor-Semiconductor Nanowire

Understand

Hybrid superconductor-semiconductor nanowires are predicted to undergo a field-induced phase transition from a trivial to a topological superconductor, marked by the closure and re-opening of the excitation gap, followed by the emergence of Majorana bound states at the nanowire ends.

• Many local density-of-states measurements have reported signatures of the topological phase, however this interpretation has been challenged by alternative explanations.
• Here, by measuring nonlocal conductance, we identify the closure of the excitation gap in the bulk of the semiconductor before the emergence of zero-bias peaks.
• This observation is inconsistent with scenarios where zero-bias peaks occur due to end-states with a trivially gapped bulk, which have been extensively considered in the theoretical and experimental literature.