Signature of the two-dimensional phonon dispersion in graphene probed by double-resonant Raman scattering

The contributions of the two-dimensional phonon dispersion to the double-resonant Raman scattering process in graphene is determined from the line shape of the two-phonon combination mode around 2450 cm(-1). This mode is usually referred to as G* or D + D ''. By combining Raman experiments with excitation energies up to 2.8 eV and a full two-dimensional calculation of the double-resonant Raman process based on fourth-order perturbation, we can describe in detail the composition of this two-phonon mode and explain the asymmetry on the high-frequency side. The asymmetry directly reflects phonon contributions with wave vectors away from the high-symmetry lines in the Brillouin zone. The main peak of this mode originates from the K Gamma high-symmetry line highlighting and supporting two important findings: first, the existence of so-called inner processes and, second, the dominant contribution along the high-symmetry line. DOI: 10.1103/PhysRevB.87.075402