Spin mixing conductance of ferromagnet/topological-insulator and ferromagnet/heavy-metal bilayers with strong interfacial spin-orbit coupling: A first-principles time-dependent quantum transport approach

Spin pumping and related phenomena have been observed recently in heavy metals and topological insulators, where the spin-orbit coupling plays an essential role. Conventional spin mixing conductance, which governs the magnitude of pumped spin current, is not well-defined when spin-orbit coupling is present directly at the interface. Nevertheless, an effective one can be extracted as the pre-factor of spin current vs. precession cone angle dependence, where we compute spin current using density functional theory combined with Floquet-nonequilibrium-Green function formalism [Phys. Rev. B 85, 05446 (2012)]. In this work we compute the spin-mixing conductance for Co/Bi₂Se₃, Co/Pt and Co/W junctions.