Electron correlation effects in the spectral momentum density of graphite

The spectral function of an annealed evaporated carbon film was measured using a high-energy (e,2e) spectrometer. Interpretation of these data was relatively straightforward due to low levels of multiple scattering. Large lifetime broadening and strong asymmetries were found in the observed line shapes, with tails extending to large binding energies. A conventional band-structure calculation within the frame of the density functional theory failed to describe the observed intensity. However it could be described well using a calculation of the spectral function based on the cumulant expansion to the single-particle Green's function. Neither the theory nor the experiment showed indications of well-defined intrinsic plasmon structures