Electronic collective excitations in AB-stacked nanographite ribbons

The inter-π-band electronic excitations of AB-stacked nanographite ribbons are studied within the self-consistent-field approach. Such excitations directly reflect the characteristics of the π-electronic structure. They depend on the magnitude (q) and the direction (θ) of the transferred momentum, the edge structure, and the stacking sequence. The loss function exhibits several peak structures. The pronounced peak, with frequency larger than 5 eV, is identified as the π-electronic collective excitations. The π plasmons exhibit highly anisotropic behavior. They are almost absent, when the transferred momentum is perpendicular to the graphitic plane (θ = 90°). However, their frequencies at small θ are not sensitive to the change in the stacking sequence.