Theory and model analysis of spin relaxation time in graphene - Could it be used for spintronics?

Graphene appears to be an excellent candidate for spintronics due to the low spin-orbit coupling in carbon, the two-dimensional nature of the graphene sheet, and the high electron mobility. However, recent experiments by Tombros et al. [Nature 448, 571 (2007).] found a prohibitively short spin-decoherence time in graphene. We present a comprehensive theory of spin decoherence in graphene including intrinsic, Bychkov-Rashba, and ripple related spin-orbit coupling. We find that the available experimental data can be explained by an intrinsic spin-orbit coupling which is orders of magnitude larger than predicted in first principles calculations. We show that comparably large values are present for structurally and electronically similar systems, MgB2 and Li intercalated graphite. The spin-relaxation in graphene is neither due to the Elliott-Yafet nor due to the Dyakonov-Perel mechanism but a smooth crossover between the two regimes occurs near the Dirac point as a function of the chemical potential. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim