University of Cambridge > > Department of Materials Science & Metallurgy Seminar Series > Magneto-optical detection of the orbital Hall effect in a light metal Ti

Magneto-optical detection of the orbital Hall effect in a light metal Ti

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Refreshments and cakes will be available!

The experimental observation of the orbital Hall effect (OHE) in a light metal Ti using the magneto-optical Kerr effect (MOKE) will be presented [1]. The OHE is the generation of electron orbital angular momentum flow transverse to an external electric field, and although circumstantial evidence has been growing, direct detection has remained elusive [2]. Previously, theoretical studies predicted that the OHE is a fundamental origin of the spin Hall effect (SHE) in many transition metals [3]. Our experimental results confirm the existence of the OHE in a light element metal Ti with an unexpectedly long orbital relaxation length, ~70 nm. We found that the MOKE signal due to the OHE -induced orbital moment is orders of magnitude larger than that due to the spin moment induced by the SHE in Ti. Moreover, we examined the torque efficiency and the orbital relaxation length using orbital torque experiments with a ferromagnet layer. This observation challenges the belief that orbital angular momentum is quenched in solids. The presentation will also discuss the potential of using the orbital degree of freedom as an information carrier and the importance of studying the orbital degree of freedom. The findings significantly impact the electrical control of magnetism and underscore the need for an improved understanding of OHE dynamics in various materials. Moreover, this presentation will also explore further directions for OHE studies using other techniques such as nitrogen-vacancy scanning and x-ray circular dichroism.

[1] Choi, Y.-G., Jo, D., Ko, K., Go, D., Kim, K.-H. Park, H. G., Kim, C., Min. B.-C., Choi, G.-M., and Lee, H.-W. Nature 619, 52-56 (2023). [2] Bernevig, B. A., Hughes, T. L. & Zhang, S. C. Orbitronics: the intrinsic orbital current in p-doped silicon. Phys. Rev. Lett. 95, 066601 (2005). [3] Kontani, H., Tanaka, T., Hirashima, D. S., Yamada, K. & Inoue, J. Giant Orbital Hall Effect in Transition Metals: Origin of Large Spin and Anomalous Hall Effects. Phys. Rev. Lett. 102, 016601 (2009).

Young-Gwan was born in Daejeon and raised in Seoul and Ansan, South Korea. He earned his M.S. degree from the Department of Physics and Photon Science at the Gwangju Institute of Science and Technology (GIST), conducting laser spectroscopy studies on charge and heat transports in condensed matters in Professor Jong-Seok Lee’s laboratory. Subsequently, he pursued his Ph.D. at the Department of Energy Science, Sungkyunkwan University (SKKU), collaborating with Professor Gyung-Min Choi on studies involving charge, spin, and orbital transports optically. Currently, Young-Gwan is a postdoctoral researcher at the Max Planck Institute for Chemical Physics of Solids (MPI-CPfS), where he studies a single spin qubit states-based quantum sensing technique (nitrogen-vacancy scanning) with Dr. Uri Vool’s group and conducts research on x-ray magnetism.

This talk is part of the Department of Materials Science & Metallurgy Seminar Series series.

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