Ab initio study of spin and momentum relaxation in Elliott-Yafet spin decoherence

In the Elliott-Yafet (EY) theory, spin decoherence near room temperature is mainly mediated by electron-phonon (e-ph) interactions. The conventional wisdom is that the EY spin and momentum relaxation times are directly proportional. This proportionality has been widely used to analyze spin relaxation mechanisms in many different materials, although it is justified only for simple model systems. Here, we use our recently developed first-principles method [1] to compute independently and analyze the e-ph spin-flip and momentum-scattering interactions. We reveal stark differences between the two, and show that the EY spin and momentum relaxation mechanisms are governed by distinct microscopic processes, both in simple materials such as silicon and diamond and in complex topological semimetals. We demonstrate that the widely used proportionality between EY spin and momentum relaxation times is inaccurate, and so is the Elliott approximation relating the two. Our results highlight the need for atomistic spin relaxation calculations that take into account the electronic wave function, spin texture, phonon modes and their mode-dependent spin-phonon interactions.

[1] J. Park, J.-J. Zhou, and M. Bernardi, arXiv:1906.01109