Ab-initio calculation of spin relaxation times

One of the most fundamental questions in spintronics to date concerns the ultimate limit of spin relaxation times. We have been developing for the first time a parameter-free first-principles method to determine spin relaxation times. Our effort initially concentrates on silicon and diamond. For liquid-nitrogen temperatures and above, spin relaxation in silicon is dominated by the Elliott-Yafet mechanism. The spin relaxation is induced by momentum scattering off impurities or phonons. The development of a basic methodology based on density-functional calculations that can be used to determine momentum scattering lifetimes has been recently completed by one of us [1]. By considering the spin-orbit mixing of the up and down states, the spin-flip matrix elements can be related to the momentum matrix elements. The underlying theory has previously been derived for III-V semiconductors with direct band gap but did previously not exist for indirect-band gap materials such as silicon or diamond. We report results of an accurate formulation to calculate spin relaxation times in silicon and diamond based on first-principles methods, which we find in excellent agreement with experimental relaxation times. Due to the ab-initio nature of our method, it can be directly applied to study other potentially spin-preserving systems.\\[4pt] [1] O. D. Restrepo et al., Appl. Phys. Lett. \textbf{94}, 212103 (2009).