Full first-principles theory of spin relaxation in group-IV materials.

We present a generally applicable parameter-free first-principles method to determine electronic spin relaxation times and apply it to the technologically important group-IV materials silicon, diamond, and graphite. We concentrate on the Elliott-Yafet mechanism, where spin relaxation is induced by momentum scattering off phonons and impurities. In silicon, we find a ~T(-3) temperature dependence of the phonon-limited spin relaxation time T(1) and a value of 4.3 ns at room temperature, in agreement with experiments. For the phonon-dominated regime in diamond and graphite, we predict a stronger ~T(-5) and ~T(-4.5) dependence that limits T(1) (300 K) to 180 and 5.8 ns, respectively. A key aspect of this Letter is that the parameter-free nature of our approach provides a method to study the effect of any type of impurity or defect on spin transport. Furthermore we find that the spin-mix amplitude in silicon does not follow the E(g)(-2) band gap dependence usually assigned to III-V semiconductors but follows a much weaker and opposite E(g)(0.67) dependence. This dependence should be taken into account when constructing silicon spin transport models.