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Topological devices as an enabler of dissipationless electronics

Quantization rule is elucidated for “Quantized Anomalous Hall Effect”

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Graduate School of Engineering / Faculty of Engineering
2014/09/02

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 the “Integer Quantum Hall Effect,” is expected to find applications in low-power-consumption electronic devices. However, the Quantum Hall Effect has a drawback in that a strong magnetic field must be applied for it to arise.

Magnetic topological insulators can host the quantum Hall effect in absence of a magnetic field, where a current flow emerges without any energy loss at the edge of the sample.

© 2014 M. S. Bahramy.
Magnetic topological insulators can host the quantum Hall effect in absence of a magnetic field, where a current flow emerges without any energy loss at the edge of the sample.

Topological insulators are a new class of semiconductor that are insulating in bulk but possesses a conducting metallic surface layer. When topological insulators are doped with magnetic ions, ferromagnetism emerges in the interior of the material . Owing to the novel interaction of the surface metallic states and ferromagnetism, magnetic topological insulators can host the quantum Hall effect in absence of a magnetic field. This is called the “Quantized Anomalous Hall Effect”, where the edge current emerges without the external application of magnetic fields. Since the Quantized Anomalous Hall Effect does not need any magnetic fields, this quantum phenomenon is expected to find applications in electric devices employing edge current.

Researchers at the Graduate School of Engineering Department of Applied Physics at the University of Tokyo, headed by Professor Yoshinori Tokura, in collaboration with former lecturer Joseph Geroge Checkelsky, PhD candidate Ryutaro Yoshimi and Professor Masashi Kawasaki, have fabricated thin films of Cr-doped magnetic topological insulator [Cr0.22(Bi0.2Sb0.8)1.78Te3]. By making a field effect transistor and measuring the Hall effect, the researchers observed the Quantized Anomalous Hall Effect. Furthermore, they have examined the Hall effect behavior under various gating electric fields and temperature ranges and have found the quantization rule of the longitudinal and transverse conductivity in the Quantized Anomalous Hall Effect is similar to that in conventional Quantum Hall Effect 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.

Press release

Paper

J. G. Checkelsky, R. Yoshimi, A. Tsukazaki, K. S. Takahashi, Y. Kozuka, J. Falson, M. Kawasaki and Y. Tokura,
“Trajectory of the anomalous Hall effect towards the quantized state in a ferromagnetic topological insulator”,
Nature Physics Online Edition: 2014/8/18 (Japan time), doi: 10.1038/nphys3053.
Article link

Links

Graduate School of Engineering

Department of Applied Physics, Graduate School of Engineering

Quantum-Phase Electronics Center, Graduate School of Engineering

Department of Applied Physics, Tokura Laboratory, Graduate School of Engineering

Center for Emergent Matter Science, RIKEN

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