Large anisotropy in the dynamic structure factor of graphite

Inelastic x-ray scattering studies of single-crystal graphite with the direction of $\overrightarrow{\mathrm{k}}$, the momentum transfer, parallel or perpendicular to the $C$ axis reveal a significant qualitative difference in the $\mathrm{}\left|k\right|\mathrm{}$ dependence of the plasmon mode. The results along the $A$ axis are similar to and reveal the same anomalies as those previously reported for Li, Be, Al, and Si. The $C$-axis results, however, are in semiquantitative agreement with mean-field-theory predictions.