The Progress of Orbitronics: The Enhancement of Orbital Torque Efficiency

Abstract

Orbitronics, focusing on the orbital degree of freedom of the electrons, is currently experiencing rapid development. Orbit-torque (OT) devices, such as OT-magnetic random-access memory and the orbital terahertz emitters, are being widely investigated for their low-power consumption and high stability in practical applications. However, the OT efficiency of these devices still requires further enhancement. In this review, we provide a concise introduction to the fundamental concepts in orbitronics, including the orbital Hall effect, orbital Rashba-Edelstein effect, and orbital-to-spin conversion coefficient. Furthermore, recent advances are highlighted for enhancing OT efficiency. These approaches can be broadly categorized into two intrinsic strategies: one focused on directly increasing orbital currents and torques, and the other aimed at improving the orbital-to-spin conversion coefficient. Additionally, we discuss current challenges and future directions in orbitronics. This review, along with the works discussed herein, aims to explore the potential applications of orbitronics in memory devices, logic computing, and terahertz emitters.