Impact of the impurity symmetry on orbital momentum relaxation and orbital Hall effect studied by the quantum Boltzmann equation

We develop a quantum Boltzmann equation approach that incorporates microscopic impurity models into the theory of orbital transport, revealing how the impurity properties, including their symmetry, influence the relaxation of orbital momentum and the orbital Hall effect. Specifically, we demonstrate that when the impurity potential has axial symmetry, the relaxation is governed by the Dyakonov-Perel mechanism. In contrast, when this symmetry is broken, scattering can result in a rapid Elliott-Yafet relaxation of orbital momentum. The details of impurity potential also affect the intrinsic orbital Hall effect even when the impurity concentration is very small. Impurities that alter the orbital texture can also give rise to a skew-scattering contribution to the orbital Hall effect, although this does not necessarily dominate in materials that are nearly pristine because of the Dyakonov-Perel relaxation.