Electron-phonon coupling-induced kinks in the sigma band of graphene

TL;DR

This study reveals that the sigma band of graphene exhibits kinks in its dispersion due to electron-phonon interactions, indicating weak coupling to substrate states and challenging previous expectations about such features.

Contribution

It demonstrates that sigma band kinks in graphene are caused by electron-phonon coupling and not Fermi-Dirac cutoff effects, highlighting weak coupling to substrate electrons.

Findings

Kinks observed in sigma band dispersion of graphene.

Kinks caused by electron-phonon interaction, not Fermi cutoff.

Weak coupling of sigma holes to substrate states.

Abstract

Angle-resolved photoemission spectroscopy reveals pronounced kinks in the dispersion of the sigma band of graphene. Such kinks are usually caused by the combination of a strong electron-boson interaction and the cut-off in the Fermi-Dirac distribution. They are therefore not expected for the $\sigma$ band of graphene that has a binding energy of more than 3.5 eV. We argue that the observed kinks are indeed caused by the electron-phonon interaction, but the role of the Fermi-Dirac distribution cutoff is assumed by a cut-off in the density of $\sigma$ states. The existence of the effect suggests a very weak coupling of holes in the $\sigma$ band not only to the $\pi$ electrons of graphene but also to the substrate electronic states. This is confirmed by the presence of such kinks for graphene on several different substrates that all show a strong coupling constant of lambda=1.