Non-Majorana-origin of the half-integer conductance quantization elucidated by multi-terminal superconductor-quantum anomalous Hall insulator heterostructure

TL;DR

This study demonstrates that the observed half-integer conductance quantization in superconductor-quantum anomalous Hall insulator heterostructures is due to potential equilibration effects, not Majorana modes, challenging previous interpretations.

Contribution

The paper introduces a multi-terminal formalism to analyze edge transport, revealing the non-Majorana origin of half-integer conductance quantization.

Findings

Half-integer conductance arises from potential equilibration at the superconductor electrode.

The formalism clarifies the origin of conductance quantization beyond simple two-terminal models.

Experimental results show no evidence of Majorana modes in the observed quantization.

Abstract

Chiral one-dimensional transport can be realized in thin films of a surface-insulating ferromagnetic topological insulator called quantum anomalous Hall insulator (QAHI). When superconducting (SC) pairing correlations are induced in the surface of such a material by putting an $s$-wave superconductor on the top, the resulting topological superconductivity gives rise to chiral Majorana edge-modes. A quantized two-terminal conductance of $\frac{1}{2}(e^2/h)$ was proposed as a smoking-gun evidence for the topological SC phase associated with a single chiral Majorana edge-mode. There have been experiments to address this proposal, but the conclusion remains unclear. Here, we formulate the edge transport in a multi-terminal superconductor-QAHI heterostructure using the Landauer-B\"uttiker formalism. Compared to the original proposal for the $\frac{1}{2}(e^2/h)$-quantization based on a simple two-terminal model, our formalism allows for deeper understanding of the origin of the quantization. The analysis of our experiments on multi-terminal devices unambiguously shows that the half-integer conductance quantization arises from the equilibration of the potentials of the incoming edge states at the SC electrode, and hence it is not of Majorana origin.