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 timeresolved photoemission spectroscopy. The lifetime was found to be inversely proportional to the excitation energy above the Fermi level, i.e., sE 2 EFd, in sharp contrast to that of metals, whose lifetime is found to be proportional to sE 2 EFd. 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.