Electron spin relaxation in graphene from a microscopic approach: Role of electron-electron interaction

Electron spin relaxation in graphene on a substrate is investigated from the fully microscopic kinetic spin Bloch equation approach. All the relevant scatterings, such as the electron-impurity, electron--acoustic-phonon, electron--optical-phonon, electron--remote-interfacial-phonon, as well as electron-electron Coulomb scatterings, are explicitly included. Our study concentrates on clean intrinsic graphene, where the spin-orbit coupling from the adatoms can be neglected. We discuss the effect of the electron-electron Coulomb interaction on spin relaxation under various conditions. It is shown that the electron-electron Coulomb scattering plays an important role in spin relaxation at high temperature. We also find a significant increase of the spin relaxation time for high spin polarization even at room temperature, which is due to the Coulomb Hartree-Fock contribution-induced effective longitudinal magnetic field. It is also discovered that the spin relaxation time increases with the in-plane electric field due to the hot-electron effect, which is different from the non-monotonic behavior in semiconductors. Moreover, we show that the electron-electron Coulomb scattering in graphene is not strong enough to establish the steady-state hot-electron distribution in the literature and an alternative approximate one is proposed based on our computation.