We show that the electron-phonon coupling strength obtained from the slopes of the electronic energy vs. wavevector dispersion relations, as often done in analyzing angle-resolved photoemission data, can differ substantially from the actual electron-phonon coupling strength due to the curvature of the bare electronic bands. This effect becomes particularly important when the Fermi level is close to a van Hove singularity. By performing {\it ab initio} calculations on doped graphene we demonstrate that, while the apparent strength obtained from the slopes of experimental photoemission data is highly anisotropic, the angular dependence of the actual electron-phonon coupling strength in this material is negligible.
@article{arxiv.0803.4031,
title = {Van Hove Singularity and Apparent Anisotropy in the Electron-Phonon Interaction in Graphene},
author = {Cheol-Hwan Park and Feliciano Giustino and Jessica L. McChesney and Aaron Bostwick and Taisuke Ohta and Eli Rotenberg and Marvin L. Cohen and Steven G. Louie},
journal= {arXiv preprint arXiv:0803.4031},
year = {2008}
}