Extrinsic Orbital Hall Effect and Orbital Relaxation in Mesoscopic Devices

Abstract: Despite recent advances in orbitronics, the influence of disorder on the orbital Hall effect and orbital relaxation mechanisms remains poorly understood. In this work, we numerically investigate the role of disorder in orbital transport within mesoscopic devices using a real-space tight-binding model on a two-dimensional square lattice that hosts atomic orbitals capable of carrying atomic orbital angular momentum. By considering devices with varying geometries--square and rectangular--and systematically tuning disorder strength, we examine the disorder effect on orbital Hall current (OHC) generation, and orbital relaxation. Our results reveal a strong dependence of the OHC and orbital Hall angle on disorder strength. In square devices, we demonstrate that the orbital Hall response can be strongly enhanced by disorder and its dependence on the disorder strength indicates the dominance of skew-scattering mechanism in the diffusive regime. In rectangular geometries, the orbital current decays exponentially with increasing device width, from which the orbital relaxation length is extracted. These findings provide critical insights into disorder-driven orbital transport phenomena and lay the foundation for designing next-generation orbitronic devices.