We obtained the spectral function of very high quality natural graphite single crystals using angle-resolved photoelectron spectroscopy. A clear separation of nonbonding and bonding bands and asymmetric lineshape are observed. The asymmetric line shapes are well accounted for by the finite photoelectron escape depth and the band structure. The extracted width of the spectral function (inverse of the photohole life time) near the $K$ point is, beyond the maximum phonon energy, approximately proportional to the energy as expected from the linear density of states near the Fermi energy. The upper bound for the electron-phonon coupling constant is about 0.2, a much smaller value than the previously reported one.

• Received 1 May 2007

DOI:https://doi.org/10.1103/PhysRevLett.100.016802