Plasmons and optical properties of semimetal graphite

The weak interlayer bonding in Bernal graphite induces low-density free car riers and thus low-frequency plasmons (< 0.2 eV). Such plasmons reveal them selves as pronounced peaks in the loss spectra and abrupt edge structures i n the reflectance spectra. The low-frequency plasmons are very sensitive to changes in temperature and momentum, mainly owing to the unique low-energy band structure. They can exist at larger momenta as temperature increases. The plasmon frequency clearly increases with temperature and momentum. The plasmon peak is broadened by temperature; furthermore, it decreases with m omentum. The calculated results are consistent with the experimental measur ements.