Electronic structure of heavily-doped graphene: the role of foreign atom states

TL;DR

This study uses density functional theory to analyze how heavy doping with foreign atoms like calcium alters graphene's electronic structure, revealing significant band structure changes and implications for electron-phonon interactions.

Contribution

It provides detailed insights into the electronic effects of heavy foreign atom doping in graphene, especially calcium, highlighting band structure modifications and their impact on electron-phonon coupling.

Findings

Calcium doping introduces Ca bands at the Fermi level in graphene.

Hybridization causes strong non-linearity in π* bands below Fermi level.

Non-linearity explains large anisotropic electron-phonon coupling measurements.

Abstract

Using density functional theory calculations we investigate the electronic structure of graphene doped by deposition of foreign atoms. We demonstrate that, as the charge transfer to the graphene layer increases, the band structure of the pristine graphene sheet is substantially affected. This is particularly relevant when Ca atoms are deposed on graphene at CaC$_{6}$ stoichiometry. Similarly to what happens in superconducting graphite intercalated compounds, a Ca bands occurs at the Fermi level. Its hybridization with the C states generates a strong non-linearity in one of the $\pi^{*}$ bands below the Fermi level, at energies comparable to the graphene E$_{2g}$ phonon frequency. This strong non-linearity, and not manybody effects as previously proposed, explains the large and anisotropic values of the apparent electron-phonon coupling measured in angular resolved photoemission.