The University of Tokyo

Japan Science and Technology Agency (JST)

Announcement Summary

A research group led by Takuya Matsuda, Academic Support Staff (PD) at the Institute for Solid State Physics and Associate Professor Ryusuke Matsunaga at the Institute for Solid State Physics, The University of Tokyo, and a research group led by Satoshi Nakatsuji, Professor and Tomoya Higo, Associate Professor at the Department of Physics, Graduate School of Science, The University of Tokyo, in collaboration with a research group led by Projectate Associate Professor Ryo Shimano at the Center for Low Temperature Science, The University of Tokyo, have reported a study of the anomalous Hall effect in a magnetic material when it is illuminated. Professor Ryo Shimano of the Cryogenic Research Center, The University of Tokyo, and his research group have succeeded for the first time in observing the ultrafast change in the anomalous Hall effect when a magnetic material is illuminated by light on a time scale of 10 trillionths of a second, demonstrating that the change can be used to elucidate the microscopic mechanism.

It is known that when an electric field is applied to a magnetic material, an electric current is generated not only in the direction parallel to the electric field but also in the perpendicular direction. This is called the anomalous Hall effect, which, unlike ordinary electrical conduction, has interesting features such as the generation of a dissipation-free current without energy loss. Recently, it has been revealed that the anomalous Hall effect is closely related to the topological properties of materials, attracting even greater attention. On the other hand, there is also an anomalous Hall effect caused by the scattering of electrons by impurities, and it is always a subject of debate which microscopic mechanism is responsible for the anomalous Hall effect whenever it is observed.

In this study, we have realized the first experiment in which a topological magnetic material is irradiated with very short pulses of light and the resulting changes in the anomalous Hall effect are investigated on a time scale of one-trillionth of a trillionth of a second. This corresponds to measuring the anomalous Hall effect in a very short period of time before the light strikes the material, causing only the electrons to receive energy and reach a high-temperature state, and then the energy is transferred to the lattice and spins. As a result, they observed a sharp 40% decrease in the anomalous Hall effect, while the normal conductivity remained almost unchanged. While this experimental result is well explained if it is due to topological properties, it is completely inconsistent if it is due to impurity scattering. In short, this study provides a new route to understanding the microscopic mechanism by investigating the anomalous Hall effect immediately after an optical pulse is applied. The anomalous Hall effect is also important as a means of reading magnetic information embedded in magnetic materials using electric current, and the clarification of the mechanism of the anomalous Hall effect change on a time scale of about 10 trillionths of a second will be an important design guideline for the development of high-speed magnetic information processing devices.

The research results have been published in the online edition of the international scientific journal Physical Review Letters on March 21, 2023 (local time).

Schematic diagram of this research

For more information, please visit the website of the Institute for Solid State Physics, The University of Tokyo.