Collective excitations of coupled electron-phonon systems are calculated for both monolayer and bilayer graphene, taking into account the non-perturbative Coulomb coupling between electronic excitations in graphene and the substrate longitudinal optical phonon modes. We find that the plasmon-phonon coupling in monolayer graphene is strong at all densities, but in bilayer graphene the coupling is significant only at high densities satisfying the resonant condition ωpl≈ωph. The difference arises from the peculiar screening properties associated with chirality of graphene. Plasmon-phonon coupling explains the measured quasi-linear plasmon dispersion in the long wavelength limit, thus resolving a puzzle in the experimental observations.
@article{arxiv.1008.0862,
title = {Plasmon-phonon coupling in graphene},
author = {E. H. Hwang and Rajdeep Sensarma and S. Das Sarma},
journal= {arXiv preprint arXiv:1008.0862},
year = {2010}
}