Strong electron-phonon coupling in the σ band of graphene

First-principles studies of the electron-phonon coupling in graphene predict a high coupling strength for the σ band with λ values of up to 0.9. Near the top of the σ band, λ is found to be ≈0.7. This value is consistent with the recently observed kinks in the σ band dispersion by angle-resolved photoemission. While the photoemission intensity from the σ band is strongly influenced by matrix elements due to sublattice interference, these effects differ significantly for data taken in the first and neighboring Brillouin zones. This can be exploited to disentangle the influence of matrix elements and electron-phonon coupling. A rigorous analysis of the experimentally determined complex self-energy using Kramers-Kronig transformations further supports the assignment of the observed kinks to strong electron-phonon coupling and yields a coupling constant of 0.6(1), in excellent agreement with the calculations.