Energy gap opening in submonolayer lithium on graphene: Local density functional and tight-binding calculations

TL;DR

This paper demonstrates that submonolayer lithium adsorption on graphene can induce an energy gap in its electronic spectrum, supported by density functional theory and tight-binding calculations, revealing potential for band gap engineering.

Contribution

It introduces a combined ab initio and tight-binding approach to show how lithium adsorption creates an energy gap in graphene, highlighting a Kekulé-type lattice distortion as the mechanism.

Findings

Lithium adsorption induces an energy gap in graphene's spectrum.

Tight-binding models with Kekulé-type distortions reproduce the gap.

Energy gap opening is possible for periodic metal compounds with multiples of 3 in composition.

Abstract

The adsorption of an alkali-metal submonolayer on graphene occupying every third hexagon of the honeycomb lattice in a commensurate $(\sqrt{3}\times\sqrt{3})R30^\circ$ arrangement induces an energy gap in the spectrum of graphene. To exemplify this type of band gap, we present \textit{ab initio} density functional theory calculations of the electronic band structure of C$_6$Li. An examination of the lattice geometry of the compound system shows the possibility that the nearest-neighbor hopping amplitudes have alternating values constructed in a Kekul\'e-type structure. The band structure of the textured tight-binding model is calculated and shown to reproduce the expected band gap as well as other characteristic degeneracy removals in the spectrum of graphene induced by lithium adsorption. More generally we also deduce the possibility of energy gap opening in periodic metal on graphene compounds C$_x$M if $x$ is a multiple of 3.