Orbitronics: Electron orbital angular momentum dynamics in metals

Abstract

Electron's orbital degrees of freedom are a crucial attribute of solids as it influences many fundamental properties of materials through spin–orbit coupling and crystal field-mediated coupling to lattice. The successful control and manipulation of spin states in solid-state systems through electron orbital angular momentum (OAM) following recent theoretical predictions has triggered an upsurge of research activities to attain enhanced functionality and efficiency in devices. This new approach, known as “orbitronics,” explores the use of OAM for information processing and storage, potentially offering significant advantages over traditional spintronics by harnessing the orbital degrees of freedom. In particular, the dynamics of OAM transport within ferromagnets is fundamentally different from that of its spin counterpart and propagates over a longer length scale than the spin dephasing length enabling long-range high-density information transmission. The advancements in the field from the fundamental understanding of OAM generation to the latest orbital-charge current interconversion techniques and long-range OAM dynamics within materials is meticulously reviewed here with insights from “orbital pumping” and Terahertz experiments. Subsequently, the recently proposed concept of exploiting OAM via orbital angular position for orbital current generation, a qualitatively different approach compared to spin angular momentum, is also introduced.