Dominant phonon wavevectors of the 2D Raman mode of graphene

We investigate the dominant phonon wavevectors q* and the associated dominant phonon-assisted electronic transitions implied by the 2D Raman mode of graphene by combining ab initio calculations with a full two-dimensional integration over the graphene Brillouin zone. We find that q* are highly anisotropic and rotate with the polarizer:analyzer condition, providing access to the entire angular extent around K. The resonant electronic transitions do not lie along the K - M - K' line and can be transformed from being apparently "inner" to "outer" with the addition of a reciprocal lattice vector, showing that both are equivalent. We thus invalidate the notion of "inner" and "outer" processes completely. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim