Low-frequency π-electronic excitations of simple hexagonal graphite

The simple hexagonal graphite exhibits novel excitation properties. The low-frequency pi -electronic excitations principally reflect the pi -band characteristics, the strong wave-vector-dependence, the highly anisotropic behavior, and the special symmetry. The plasmon frequency increases with momentum, while the opposite is true for the intensity of plasmon peak. The low-frequency plasmon behaves as the optical plasmon in a 3D electron gas. The main differences between plasmons parallel and perpendicular to the graphite planes are very special. The former have higher plasmon frequencies. However, their plasmon peaks and critical momenta are much lower than those of the latter. Doping leads to significant changes in the pi -electronic excitations, such as the great enhancement of plasmon frequency and plasmon peak. The electronic excitations of the simple hexagonal graphite quite differ from those in the Bernal graphite or the 2D graphite sheet.