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.