Ab initio spatio-temporal spin transport in a density-matrix formalism*

Ab initio design of materials and devices for spintronics requires simulation of spin dynamics and spatial transport in realistic device geometries, accounting for both coherent and incoherent processes. Combining density-matrix quantum dynamics with semi-classical spatial transport within the Wigner function formalism, we develop a computational framework for simulating spatio-temporal spin dynamics and transport. This framework accounts for electron-phonon, electron-electron, and electron-impurity scatterings at device length scales using a Lindbladian formalism applied to ab initio density matrices. The Wigner function formalism allows resolution of physical properties such as spin in phase space, with real and reciprocal space resolution, which also provides significant opportunities for parallelization that we leverage for an efficient GPU-enabled implementation targeting exascale computing resources. Using this approach, we showcase dephasing effects due to transport in spintronic devices, investigating the impact of spin textures including Rashba and persistent spin helix textures on the spin mixing in reciprocal space.