Zero Bias Conductance Peak in Dirac Semimetal-Superconductor Devices

TL;DR

This study observes a large zero-bias conductance peak in Dirac semimetal-superconductor devices, attributing it to supercurrent effects rather than Majorana zero modes, thus cautioning against misinterpretation in topological quantum computing experiments.

Contribution

The paper demonstrates that a large ZBCP in Dirac semimetal-superconductor junctions can arise from supercurrent effects, not MZMs, providing new criteria to distinguish these phenomena.

Findings

Large ZBCP observed close to four times the normal conductance.

ZBCP attributed to supercurrent effects, not Majorana modes.

Supercurrent effects observed over unusually long distances.

Abstract

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.