August 13, 2025• Physics 18, s99
Edge currents are observed in a magnetic topological insulator even when conventional theory says that they should not.
G. M. Ferguson et al. [1]
G. M. Ferguson et al. [1]
Magnetic topological insulators (MTIs) are predicted to conduct electricity along their surfaces but act as insulators in their interior, a promising property for next-generation computing platforms. At low temperatures, MTIs can host the quantum anomalous Hall effect (QAHE). Discovered in 2013, the QAHE manifests as a quantized transverse conductivity when a current flows through a ferromagnetic slab without an external magnetic field. Now George Ferguson and Katja Nowack of Cornell University and their colleagues have observed that, contrary to expectations, edge currents in an MTI slab are present even after its quantized conductivity breaks down [1]. MTIs attract interest in part because their surface currents are expected to flow without dissipation, a boon for energy-efficient devices.
In 2023, members of the research team observed that, under a low bias current that sustained the QAHE, bulk rather than edge currents dominated electronic transport in an MTI [2]. The result was surprising because the currents that generate the QAHE are often assumed to be confined to the sample edges. In the new experiment, the team used scanning superconducting quantum interference device microscopy to measure the current distribution in the same MTI samples but with a larger bias current that quashed the QAHE. In contrast to the previous experiment, the team observed current concentrated near the sample’s edges, which coexisted with a larger current distributed uniformly across the device width.
The team’s models suggest that the observed edge currents arose from changes in magnetization brought on by gradients in electrostatic and chemical potential. The researchers say that the work will guide future studies geared toward clarifying the connection between topologically protected surface states and other electronic phenomena in MTIs.
–Rachel Berkowitz
Rachel Berkowitz is a Corresponding Editor for Physics Magazine based in Vancouver, Canada.
ReferencesG. M. Ferguson et al., “Local potential distribution generates edge currents in a magnetic topological insulator,” Phys. Rev. B 112, 075414 (2025).G. M. Ferguson et al., “Direct visualization of electronic transport in a quantum anomalous Hall insulator,” Nat. Mater. 22 (2023).Subject AreasRelated Articles
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