  Majorana 'zero-modes' are expected to be immune to decoherence. The primary
method for their characterization in a 1D topological superconductor, is
measuring the tunneling current into the edge of the superconductor. Presently,
the hallmark of a localized Majorana edge-state is an emergent quantized
zero-bias conductance peak (ZBCP). However, such a conductance peak can also
result from other mechanisms; e.g., crossing (and sticking) of two branches of
a standard Andreev bound state, or a soft potential at the edge of the
superconductor. Since the emergence of a 'Majorana-ZBCP' must be accompanied by
an opening of a topological gap in the bulk, we performed two simultaneous
tunneling measurements: one in the bulk and another at the edge of the 1D
superconductor. Measurements were performed with an InAs nanowire in-situ
coated with epitaxial aluminum. For particular gate-tuning of the chemical
potential in the wire and a Zeeman field parallel to the wire, we observed a
closing of the superconducting bulk-gap followed by its reopening concomitant
with the appearance of a ZBCP at the edge. We note that a ZBCP could also be
observed with different tuning parameters without an observed reopening of the
bulk-gap. This demonstrates the importance of simultaneous probing of the bulk
and edge when searching for a Majorana edge-state.
