Bulg. J. Phys. vol.38 no.1 (2011), pp. 072-084

Non-Adiabatic Phonon Dispersion of Graphene

V.N. Popov
Faculty of Physics, University of Sofia, BG-1164 Sofia, Bulgaria
Abstract. Recently, failure of the adiabatic approximation has been observed in the charge doping dependence of the Raman spectrum of graphene. The theoretical work has been limited to the phonon dispersion modification in the vicinity of the Brillouin zone center. Here, we present estimation of the non-adiabatic effects on the phonons close to the K point of the Brillouin zone obtained by a perturbation scheme within a non-orthogonal tight-binding model. We show that the explicit account of the dynamic effects change the shape of the Kohn anomaly of the TO phonon branch at the K point. The increase of the charge doping level essentially removes the Kohn anomaly. These results are important for modelling phenomena, in which phonons at the K point are involved, e.g., defect- and second-order Raman scattering.

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