Electric-Field Effects on Spin Diffusion Length in Solids: An Ab Initio Approach Beyond the Drift-Diffusion Model

Abstract

Understanding how a longitudinal electric field governs spin transport is of both fundamental and practical importance for spintronics, yet a general, parameter-free simulation framework and a comprehensive microscopic understanding of this process remain elusive. We develop an ab initio quantum master equation approach─with quantum treatment of electron scattering processes─to simulate the spin diffusion length (ls) under longitudinal fields in representative spintronic materials. While the standard drift-diffusion model adequately describes the Elliott–Yafet system monolayer WSe2, it introduces large errors in D’yakonov-Perel’ systems GaAs, GaN, and graphene-h-BN heterostructure, owing primarily to field-induced spin precession dynamics and zero-field spatial spin precession. To dissect these mechanisms, we derive an ab initio matrix-drift-diffusion (ab-mDD) model, which substantially improves accuracy for GaAs and GaN while yielding transparent physical insights. In heavily doped graphene-h-BN, we identify an additional mechanism: the electric field significantly modifies the homogeneous steady-state density matrix away from the Fermi–Dirac function, thereby altering the scattering dynamics and further affecting ls─an effect absent in prior treatments. This work establishes a broadly applicable and transparent first-principles methodology for simulating and analyzing field-driven spin transport in solids and provides new mechanistic insights for designing electrically tunable spintronic devices.