Terahertz plasmon and infrared coupled plasmon-phonon modes in graphene

Plasmon and coupled plasmon-phonon modes of Dirac particles in graphene are investigated theoretically within the diagrammatic self-consistent field theory. It shows that two terahertz plasmon modes and four infrared coupled plasmon-phonon modes can be achieved via intra- and inter-band transitions in graphene. We find that with increasing q and carrier density, the plasmon modes are strongly coupled with optic-phonon modes in graphene in the infrared region. The coupled plasmon-phonon modes exhibit some interesting features which can be utilized to realize the plasmonic devices. Our results suggest that the carrier-phonon interaction should be considered to understand and explain the properties of elementary electronic excitations in graphene.