Modeling Electromagnetic Field Dependent Spatio-temporal Transport from First Principles

Engineering materials and devices for spintronics requires first principles prediction of spin transport accounting for both coherent processes such as spin precession and incoherent processes such as electron-phonon scattering. We recently formulated ab initio density-matrix transport as a semi-local limit to Wigner function transport and used it to predict spatially-resolved charge and spin transport on realistic device length scales. This approach has accurately predicted spin diffusion length and dephasing profiles in several systems, including Rashba and persistent spin helix materials, but has not accounted for the effect of electric and magnetic fields. Here, we extend the semi-local limit of Wigner transport to derive the terms for coupling to electromagnetic fields. We show that the fields simultaneously introduce semi-classical momentum-space advection terms due to the forces on the electron, similar to the Boltzmann transport equation, as well as Stark and Zeeman-like perturbations to the Liouville equation in addition to other fundamentally quantum-mechanical effects. We apply this framework to investigate the impacts of electric and magnetic fields on spin transport in materials with varying symmetries and nature of spin-orbit coupling.