  Majorana zero modes (MZMs), fundamental building blocks for realizing
topological quantum computers, can appear at the interface between a
superconductor and a topological material. One of the experimental signatures
that has been widely pursued to confirm the existence of MZMs is the
observation of a large, quantized zero-bias conductance peak (ZBCP) in the
differential conductance measurements. In this Letter, we report observation of
such a large ZBCP in junction structures of normal metal (titanium/gold Ti/Au)
+ Dirac semimetal (cadmium arsenide Cd3As2) + conventional superconductor
(aluminum Al), with a value close to four times that of the normal state
conductance. Our detailed analyses suggest that this large ZBCP is most likely
not caused by MZMs. We attribute the ZBCP, instead, to the existence of a
supercurrent between two far-separated superconducting Al electrodes, which
shows up as a zero-bias peak because of the circuitry and thermal fluctuations
of the supercurrent phase, a mechanism conceived by Ivanchenko and Zil'berman
more than 50 years ago [JETP 28, 1272 (1969)]. Our results thus call for
extreme caution when assigning the origin of a large ZBCP to MZMs in a
multiterminal semiconductor or topological insulator/semimetal setup. We thus
provide criteria for identifying when the ZBCP is definitely not caused by an
MZM. Furthermore, we present several remarkable experimental results of a
supercurrent effect occurring over unusually long distances and clean perfect
Andreev reflection features.
