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.