Speaker: Young-Gwan Choi, Post-Doctoral Researcher, Max Planck Institute for Chemical Physics of Solids, Dresden, Germany.

The experimental observation of the orbital Hall effect (OHE) in a light metal Ti using the magneto-optical Kerr effect (MOKE) will be presented. 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. Previously, theoretical studies predicted that the OHE is a fundamental origin of the spin Hall effect (SHE) in many transition metals. 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.

http://talks.cam.ac.uk/talk/index/216436