# Signatures of adatom effects in the quasiparticle spectrum of Li-doped graphene

## TL;DR

This study reveals how lithium adatoms affect the electronic spectrum of graphene, creating impurity bands and increasing quasiparticle scattering, which are crucial for understanding ARPES measurements and electronic properties in doped graphene.

## Contribution

It introduces an atomistic T-matrix formalism to analyze adatom-induced spectral effects and identifies the formation of a lithium-induced impurity band in graphene.

## Key findings

- Li adatoms create a low-energy impurity band at the Γ point.
- Impurity band depends on Li concentration and aligns with the Fermi level at 8%.
- Quasiparticle scattering increases above 1 eV near the van Hove singularity.

## Abstract

We study the spectral function and quasiparticle scattering in Li-decorated graphene (Li@graphene) with an atomistic $T$-matrix formalism and uncover adatom-induced spectral effects which shed light on experimentally observed angle-resolved photoemission spectroscopy (ARPES) features. From transport studies, alkali adatoms are known to introduce charged-impurity scattering limiting the carrier mobility. Here, we demonstrate that Li adatoms furthermore give rise to a low-energy impurity band centered at the $\Gamma$ point which originates from the hybridization between the atomic 2s state of the Li adatoms and graphene "surface" states. We show that the impurity band is strongly dependent on the concentration $c_\mathrm{Li}$ of Li adatoms, and aligns with the Li-induced Fermi level on the Dirac cone at $c_\mathrm{Li}\sim 8\,\%$ ($E_F\approx 1.1\,\mathrm{eV}$). Finally, we show that adatom-induced quasiparticle scattering increases dramatically at energies above $\sim 1\,\mathrm{eV}$ close to the van Hove singularity in the graphene density of states (DOS), giving rise to a large linewidth broadening on the Dirac cone with a concomitant downshift and a characteristic kink in the conduction band. Our findings are highly relevant for future studies of ARPES, transport, and superconductivity in adatom-doped graphene.