Ab initio study of 2D plasmon enhancement in alkali intercalated graphene on metallic substrates

Alkali metal (AM) atoms, (e.g. in LiC₂ or CsC₈) donate electrons to the graphene π band causing the appearance of the strong Dirac plasmon (DP) in the EEL spectra. At the same time, the AM σ band remains partially filled and supports another 2D plasmon, which hybridizes with the Dirac plasmon causing appearance of the weak linearly dispersive plasmon, known as the acoustic plasmon (AP) [1,2]. We present the results of a theoretical simulation of alkali atoms intercalated between the graphene and a metallic substrate (e.g. Ir(111) or Al(111)) and forming a periodic superlattice, which causes a huge enhancement of DP and AP. Moreover the AP intensity and Fermi velocity strongly depend on graphene/substrate separations. This enhancement mechanism, in addition to its very interesting fundamental aspect, suggests many possibilities for plasmonic applications. The theoretical simulation is performed using a state of the art DFT (ground state) + RPA (excited state) technique, adapted for the study of the dielectric properties in large multilayer heterostructures, which completely exclude inter-supercell Coulomb interaction.
[1] L. Marušić and V. Despoja, Phys. Rev. B 95 (2017) 201408(R)
[2] V.Despoja and L. Marušić, Phys. Rev. . B 97 (2018) 205426