Sharp contrasts in low-energy quasiparticle dynamics of graphite between brillouin zone K and H points

The low-energy quasiparticle (QP) dynamics of graphite are governed by a coupling with the E2g longitudinal optical phonon of ωLO 200meV, which is found to dramatically depend on the electronic band dispersion εk. A discontinuity of the QP linewidth develops near ωLO for a linear band with a quadratic band top [near the Brillouin zone (BZ) K point], while it disappears for a pure linear band (near the BZ H point). It is also found that the effective electron-phonon coupling near the K point is stronger than near the H point by more than 50%. This finding makes possible a consistent understanding of recent angle-resolved photoemission observations near the K point.