Coulomb excitations in AA- and AB-stacked bilayer graphites

The pi-electronic excitations are studied for the AA- and AB-stacked bilayer graphites within the linear self-consistent-field approach. They are strongly affected by the stacking sequence, the interlayer atomic interactions, the interlayer Coulomb interactions, and the magnitude of the transferred momentum. However, they hardly depend on the direction of the transferred momentum and the temperature. There are three low-frequency plasmon modes in the AA-stacked system but not the AB-stacked system. The AA- and AB-stacked plasmons exhibit the similar pi plasmons. The first low-frequency plasmon behaves as an acoustic plasmon, and the others belong to optical plasmons. The bilayer graphites quite differ from the monolayer graphite and the AB-stacked bulk graphite, such as the low-frequency plasmons and the small-momentum pi plasmons.