Plasmon Excitations for a Coulomb-coupled Graphene Layer and a Thick Conductor

Self-consistent field theory is used to obtain the plasmon dispersion relation of monolayer graphene which is Coulomb coupled to a thick conductor. We calculate numerically the undamped plasmon excitation spectrum for arbitrary wave number. For gapped graphene, both the low-frequency (acoustic) and high frequency (surface) plasmons may lie within the opening within the particle-hole region. Additionally, we obtain plasmon excitations in a region of the frequency-wave vector space which does not exist for free standing gapped graphene.