A quantum anomalous Hall (QAH) insulator is a topological phase in which the interior is insulating but electrical current flows along the edges of the sample in either a clockwise or counterclockwise direction, as dictated by the spontaneous magnetization orientation. Such a chiral edge current eliminates any backscattering, giving rise to quantized Hall resistance and zero longitudinal resistance. Here we fabricate mesoscopic QAH sandwich Hall bar devices and succeed in switching the edge current chirality through thermally assisted spin–orbit torque (SOT). The well-quantized QAH states before and after SOT switching with opposite edge current chiralities are demonstrated through four- and three-terminal measurements. We show that the SOT responsible for magnetization switching can be generated by both surface and bulk carriers. Our results further our understanding of the interplay between magnetism and topological states and usher in an easy and instantaneous method to manipulate the QAH state.
“Achieving instantaneous electrical control over the edge current chirality [direction] in QAH materials, without the need for sweeping the external magnetic field, is indispensable for the advancement of QAH-based computation and information technologies,” he said.
[...] Finding ways to to exploit these dissipation-less “chiral edge currents,” as they are known, could have far-ranging applications in quantum metrology, spintronics, and topological quantum computing. The idea was given a boost by the discovery that thin films of magnetic materials exhibit similar behavior without the need for a strong external magnetic field—something known as the quantum anomalous Hall effect (QAH)—which makes building electronic devices that harness the phenomenon much more practical.
One stumbling block has been that switching the direction of these edge currents—a crucial step in many information-processing tasks—could be done only by passing an external magnetic field over the material. Now, researchers at Penn State University have demonstrated for the first time that they can switch the direction by simply applying a pulse of current.
"Electrical switching of the edge current chirality in quantum anomalous Hall insulators" (2023) https://www.nature.com/articles/s41563-023-01694-y :
"Researchers Simplify Switching for Quantum Electronics" (2023) https://spectrum.ieee.org/amp/hall-effect-2666062907 :
Quantum anomalous Hall effect: https://en.wikipedia.org/wiki/Quantum_anomalous_Hall_effect