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

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-Büttiker 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.

Final version to appear in PRB; 10 pages, 5 figures. The raw data are available at the online depository Zenodo with the identifier https://zenodo.org/records/14176676