Department of Energy Science, Sungkyunkwan University, Suwon, Korea.
Department of Physics, Pohang University of Science and Technology, Pohang, Korea.
Nature. 2023 Jul;619(7968):52-56. doi: 10.1038/s41586-023-06101-9. Epub 2023 Jul 5.
The orbital Hall effect refers to the generation of electron orbital angular momentum flow transverse to an external electric field. Contrary to the common belief that the orbital angular momentum is quenched in solids, theoretical studies predict that the orbital Hall effect can be strong and is a fundamental origin of the spin Hall effect in many transition metals. Despite the growing circumstantial evidence, its direct detection remains elusive. Here we report the magneto-optical observation of the orbital Hall effect in the light metal titanium (Ti). The Kerr rotation by the orbital magnetic moment accumulated at Ti surfaces owing to the orbital Hall current is measured, and the result agrees with theoretical calculations semi-quantitatively and is supported by the orbital torque measurement in Ti-based magnetic heterostructures. This result confirms the orbital Hall effect and indicates that the orbital angular momentum is an important dynamic degree of freedom in solids. Moreover, this calls for renewed studies of the orbital effect on other degrees of freedom such as spin, valley, phonon and magnon dynamics.
轨道霍尔效应是指在外加电场作用下电子轨道角动量流的产生。与通常认为的固体中轨道角动量被猝灭的观点相反，理论研究预测轨道霍尔效应可以很强，并且是许多过渡金属中自旋霍尔效应的基本起源。尽管越来越多的间接证据表明了这一点，但它的直接检测仍然难以实现。在这里，我们报告了轻金属钛（Ti）中轨道霍尔效应的磁光观测。测量了由于轨道霍尔电流在 Ti 表面积累的轨道磁矩引起的克尔旋转，结果与理论计算半定量一致，并得到了基于 Ti 的磁性异质结构中的轨道力矩测量的支持。这一结果证实了轨道霍尔效应，并表明轨道角动量是固体中的一个重要动力学自由度。此外，这呼吁对其他自由度（如自旋、谷、声子和磁子动力学）的轨道效应进行重新研究。
