Electron-phonon coupling and intrinsic bandgap in highly-screened graphene

Photoemission studies of graphene have resulted in a long-standing controversy concerning the strength of the experimental electron-phonon (el-ph) interaction in comparison with theoretical calculations. Using high-resolution angle-resolved photoemission spectroscopy we study graphene grown on a copper substrate, where the metallic screening of the substrate substantially reduces the electron-electron interaction, simplifying the comparison of the el-ph interaction between theory and experiment. By taking the nonlinear bare bandstructure into account, we are able to show that the strength of the el-ph interaction shows better agreement with theoretical calculations. In addition, we observe a significant bandgap at the Dirac point of graphene.