ENERGY-DEPENDENCE OF ELECTRON LIFETIME IN GRAPHITE OBSERVED WITH FEMTOSECOND PHOTOEMISSION SPECTROSCOPY

The energy dependence of the electron lifetime in graphite was measure d using femtosecond time-resolved photoemission spectroscopy. The life time was found to be inversely proportional to the excitation energy a bove the Fermi level, i.e., (E - E(F))(-1), in sharp contrast to that of metals, whose lifetime is found to be proportional to (E - E(F))(-2 ). The results are in agreement with the prediction of the layered ele ctron gas theory, which suggests that electron-plasmon interactions do minate the lifetime of electrons in a layered electron gas, even for s mall excitation energies, due to interlayer plasmon coupling.