Manipulating spin for quantum information and spintronic devices requires quantitative prediction of quantum transport over long time and length scales. We introduce a computational framework for first-principles density-matrix quantum transport within the Wigner function formalism that facilitates spin dynamics and transport simulations, while accounting for electron-phonon scattering at device length scales. This allows us to elucidate the impact of realistic spin-orbit fields, such as Rashba and persistent spin helix, on coherent spin transport in several materials, as well as the transition to incoherent transport with increasing strength of electron-phonon scattering. We identify three distinct regimes of incoherent spin transport corresponding to the free induction decay, Dyakonov-Perel, and Elliott-Yafet regimes of spin relaxation, and find a scattering-strength-independent spin diffusion length within the Dyakonov-Perel regime. With applied magnetic fields, spin transport in this regime is sensitive to scattering strength and leads to asymmetric Hanle curves that probe the internal spin-orbit field of the material.

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• Quantum transport
• Rashba coupling
• Spin
• First-principles calculations