  Experimental spin relaxation times in graphene, critical for spintronics and
quantum information technologies, are two orders of magnitude below previous
theoretical predictions for spin-phonon relaxation. Here, ab initio
density-matrix dynamics simulations reveal that electric fields and substrates
strongly reduce spin-phonon relaxation time to the nanosecond scale, in
agreement with experiments. Our predicted out-of-plane to in-plane lifetime
ratio exceeds 1/2 on boron nitride substrates, matching experiment unlike
previous models, suggesting that spin-phonon relaxation is dominant in graphene
at room temperature.
