Van Hove Singularity and Apparent Anisotropy in the Electron-Phonon Interaction in Graphene

TL;DR

This paper reveals that the apparent anisotropy in electron-phonon interactions in graphene, derived from photoemission data, can be misleading due to band curvature effects near van Hove singularities, while the true coupling is nearly isotropic.

Contribution

It demonstrates through ab initio calculations that the actual electron-phonon coupling in graphene is isotropic despite apparent anisotropy in experimental data.

Findings

Apparent anisotropy arises from band curvature effects.

Actual electron-phonon coupling is nearly isotropic.

Near van Hove singularities, the discrepancy is significant.

Abstract

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.