  We theoretically investigate spin dynamics in spin-orbit-coupled materials.
In the ballistic limit, the spin lifetime is dictated by dephasing that arises
from energy broadening plus a non-uniform spin precession. For the case of
clean graphene, we find a strong anisotropy with spin lifetimes that can be
short even for modest energy scales, on the order of a few ns. These results
offer deeper insight into the nature of spin dynamics in graphene, and are also
applicable to the investigation of other systems where spin-orbit coupling
plays an important role.
