Orbitronics: Mechanisms, Materials and Devices

Abstract

Spintronics has been extensively explored over the past decades, focusing primarily on the spin characteristic of the electron, while the orbital feature of the electron has been conventionally assumed to be quenched by the crystal field effect. Recently, studies have unveiled a fascinating discovery that orbital current, originating from orbital effects, can be generated in materials with weak spin-orbit coupling by applying electric fields, enabling the manipulation of the ferromagnetic magnetization and induction of terahertz emission. This review highlights recent achievements in orbital effects, materials, and devices, beginning by discussing the mechanisms underlying orbital effects, e.g. the orbital Hall effect, orbital Rashba-Edelstein effect, inverse orbital Hall effect, and inverse orbital Rashba-Edelstein effect. Subsequently, a wide range of materials exhibiting orbital effects are classified and the orbital sources in them are identified. Furthermore, the review introduces the orbital torque devices and the orbital terahertz emitters, summarizing the in-depth mechanisms of the orbital torque, orbital torque efficiency, and orbital diffusion length across various material structures. Additionally, the review presents strategies for enhancing orbital torque efficiency and driving magnetization switching. These efforts aim to explore the potential applications for orbitronic memory devices, computing components, and terahertz emitters.