ABSTRACT
AA-stacking configuration has the highest symmetry, that is, the carbon atoms of one layer are directly above/below those of another layer. It has been found that AA-stacking bilayer configuration is normally encountered in the synthesis procedure of multilayer graphenes and is very difficult to distinguish from a single-layer graphene by scanning tunneling microscopy. The highly symmetric AA-stacked graphene is formed by perpendicularly stacking graphene sheets along the z^ direction. Scanning tunneling spectroscopy experiments have verified the two Dirac cones in AA-stacked bilayer grapheme. AA-stacked graphenes exhibit rich and unique plasmon spectra under the influence of dynamic Coulomb interactions. In the AA-stacked bilayer graphene, the two plasmon modes are enclosed by SPE boundaries in the low and middle regions. In general, the other pristine graphene systems, for example, the monolayer and AB-stacked graphenes, are semiconducting and only create interband electron-hole excitations, but not the low-frequency plasmons.
