Electron–phonon interaction and relaxation time in graphite

The electron–phonon (e–ph) interaction and the relaxation time of photo-excited electrons are calculated in graphite within the tight-binding scheme. The e–ph matrix element thus obtained, shows anisotropy in k-space. The calculated relaxation time is of the same order of magnitude as the experimental one. Moreover, below an energy close to the Fermi energy, the absorption rate exceeds the emission rate, which indicates that graphite can emit far infra-red electro-magnetic waves by absorbing heat. We also compare this result with Planckʹs formula for black-body radiation.