Kohn anomaly and interplay of electron-electron and electron-phonon interactions in epitaxial graphene

Abstract

The interplay of electron-phonon (el-ph) and electron-electron (el-el) interactions in epitaxial graphene is studied by directly probing its electronic structure. We found a strong coupling of electrons to the soft part of the ${A}_{1g}$ phonon evident by a kink at $150\ifmmode\pm\else\textpm\fi{}15\text{ }\text{meV}$, while the coupling of electrons to another expected phonon ${E}_{2g}$ at 195 meV can only be barely detected. The possible role of the el-el interaction to account for the enhanced coupling of electrons to the ${A}_{1g}$ phonon, and the contribution of el-ph interaction to the linear imaginary part of the self-energy at high binding energy are also discussed. Our results reveal the dominant role of the ${A}_{1g}$ phonon in the el-ph interaction in graphene and highlight the important interplay of el-el and el-ph interactions in the self-energy of graphene.