Tuning Layer Orbital Hall Effect via Spin Rotation in Ferromagnetic Transition Metal Dichalcogenides

Abstract

Orbitronics, which leverages the angular momentum of atomic orbitals for information transmission, provides a novel strategy to overcome the limitations of electronic devices. Unlike electron spin, orbital angular momentum (OAM) is strongly influenced by crystal field effects and band topology, making its orientation difficult to manipulate with external fields. In this work, by using first principle calculations, we investigate quantum anomalous Hall insulators (QAHIs) as a model system to study the layer orbital Hall effect (OHE). Due to band inversion, only one valley remains orbital polarization, and thus the OHE originates from a single valley. Based on stacking symmetry analysis, we investigated both AA and AB stacking configurations, which possess mirror and inversion symmetries, respectively. The excitation of OAM exhibits valley selectivity, determined jointly by valley polarization and orbital polarization. In AA stacking, the absence of inversion center gives rise to intrinsic orbital polarization, leading to OAM excitations from different valleys in the two layers. In contrast, AB stacking is protected by inversion symmetry, which enforces valley polarization and causes OAM in both layers to originate from the same valley. Furthermore, the direction of spin polarization tunes the sign of the Berry curvature, thereby dictating the transport of OAM. As a result, in bilayer antiferromagnetic QAHI systems, orbital currents display a distinct layer-contrasting behavior in both flow direction and OAM accumulation.