ABSTRACT
Plasmons in monolayer graphene have attracted fundamental interest stemming from electronic excitations of massless Dirac fermions. At zero temperatures, there are no intrinsic plasmons in a monolayer graphene due to the absence of free carriers. In general, a doped monolayer graphene sharply contrasts with a 2D electron gas corresponding to a quantum well in Coulomb excitations. The interlayer Coulomb interactions result in the coupling of the 2D q/q-dependent plasmon modes in the two decoupled monolayer graphenes. The low-frequency graphene plasmons have attracted considerable interest from both theoretical and experimental research; they have been found to be strongly dependent on temperature and doping free carrier density by inelastic X-ray scattering and electron energy loss spectroscopy. The double-layer model could be generalized to the superlattices of graphite intercalation compounds, in which the latter are identified to be successful in fully comprehending the low-frequency Coulomb excitations of the acceptor-/donor-type layered systems.
