Imaging signatures of edge currents in a magnetic topological insulator

TL;DR

This study uses magnetic imaging to visualize and analyze the coexistence of bulk and edge currents in a magnetic topological insulator, revealing complex transport behaviors beyond simple edge conduction.

Contribution

It introduces a model linking magnetization changes to electrochemical potential, providing new insights into current distribution in magnetic topological insulators.

Findings

Edge currents change with magnetic field reversal

Bulk and edge currents coexist at high bias

Magnetization changes explain edge current behavior

Abstract

Magnetic topological insulators (MTIs) host topologically protected edge states, but the role that these edge states play in electronic transport remains unclear. Using scanning superconducting quantum interference device (SQUID) microscopy, we performed local measurements of the current distribution in a quantum anomalous Hall (QAH) insulator at large bias currents, where the quantization of the conductivity tensor breaks down. We find that bulk currents in the channel interior coexist with edge currents at the sample boundary. While the position of the edge current changes with the reversal of the magnetic field, it does not depend on the current direction. To understand our observations, we introduce a model which includes contributions from both the sample magnetization and currents driven by chemical potential gradients. To parameterize our model, we use local measurements of the chemical potential induced changes in the sample magnetization. Our model reveals that the observed edge currents can be understood as changes in the magnetization generated by the electrochemical potential distribution in the sample under bias. Our work underscores the complexity of electronic transport in MTIs and highlights both the value and challenges of using magnetic imaging to disentangle various contributions to the electronic transport signatures.