Double resonant Raman spectra in graphene and graphite: A two-dimensional explanation of the Raman amplitude

We report calculated Raman spectra of the D and 2D modes in graphene and graphite. Evaluating the Raman amplitude in the two-dimensional Brillouin zone, we reproduce the splitting of the modes when going from single-layer graphene to graphite. The energy dependence of the D mode in graphene is 24%-32% smaller than in graphite. We discuss the intensity of the D line and show that the double resonant phonons originate from the low-symmetry parts of the Brillouin zone.