We calculate hybridization of plasmons and intrinsic optical phonons in graphene by using the self-consistent linear response formalism. We find that longitudinal plasmons (transverse magnetic modes) couple exclusively to transverse optical phonons, whereas graphene's transverse plasmons (transverse electric modes) couple only to longitudinal optical phonons. This mixing of polarizations is in contrast to the usual plasmon-phonon coupling in other systems. The resulting change in phonon frequencies increases (decreases) for transverse (longitudinal) phonons by increasing the concentration of charge carriers.
@article{arxiv.1010.4871,
title = {Unconventional plasmon-phonon coupling in graphene},
author = {M. Jablan and M. Soljačić and H. Buljan},
journal= {arXiv preprint arXiv:1010.4871},
year = {2015}
}