Topological devices as an enabler of dissipationless electronics ー Quantization rule is elucidated for “Quantized Anomalous Hall Effect” ー


When a strong magnetic field is applied to a layered semiconductor device, a current flow emerges without any energy loss at the edge of the sample (edge current). This phenomenon, called “Integer Quantum Hall Effect”, has been actually used as resistance standard and is expected to explore low-power-consumption electronic devices. However, Quantum Hall Effect has a drawback that a strong magnetic field must be applied. Topological insulators are a new class of semiconductor that is insulating in bulk but possesses a conducting metallic surface layer. When topological insulators are doped with magnetic ions, there emerges ferromagnetism. Owing to the novel interaction of the surface metallic states and ferromagnetism, magnetic topological insulators can host the quantum Hall effect in absence of magnetic field. This is called “Quantized Anomalous Hall Effect”, where the edge current emerges without magnetic fields. Since the Quantized Anomalous Hall Effect does not need any magnetic fields, this quantum phenomenon is expected to be applied to the electric devices employing the edge current.

Research group have fabricated thin films of Cr-doped magnetic topological insulator[Cr0.22(Bi0.2Sb0.8)1.78Te3]. By making the field effect transistor and measuring the Hall effect, they have observed the Quantized Anomalous Hall Effect. Furthermore, they have examined the Hall effect behavior under various gating electric field and temperature region to experimentally demonstrate that the Quantized Anomalous Hall Effect can be understood as the same quantized phenomenon as the conventional Quantum Hall Effect. These results will trigger further research towards deeper understanding of the Quantized Anomalous Hall Effect and more importantly towards realization of dissipationless electronic devices making use of the edge current generated even without magnetic fields.