Energy Dependence of Electron Lifetime in Graphite Observed with Femtosecond Photoemission Spectroscopy

The energy dependence of the electron lifetime in graphite was measured using femtosecond time-resolved photoemission spectroscopy. The lifetime was found to be inversely proportional to the excitation energy above the Fermi level, i.e., (E-EF)^-1, in sharp contrast to that of metals, whose lifetime is found to be proportional to (E-EF)^-2. The results are in agreement with the prediction of the layered electron gas theory, which suggests that electron-plasmon interactions dominate the lifetime of electrons in a layered electron gas, even for small excitation energies, due to interlayer plasmon coupling.