Making ARPES Measurements on Corrugated Monolayer Crystals: Suspended Exfoliated Single-Crystal Graphene

TL;DR

This paper develops a method to measure the electronic band structure of free-standing, corrugated monolayer graphene using ARPES, revealing that despite surface roughness, its electronic properties closely resemble ideal graphene.

Contribution

It introduces an analytical approach to relate surface corrugation to photoemission linewidth, enabling accurate bandstructure measurements of suspended graphene.

Findings

Graphene's electronic structure remains nearly ideal despite corrugation.

Suspended graphene behaves as a marginal Fermi-liquid.

Dirac point is within 25 meV of the Fermi level.

Abstract

Free-standing exfoliated monolayer graphene is an ultra-thin flexible membrane, which exhibits out of plane deformation or corrugation. In this paper, a technique is described to measure the band structure of such free-standing graphene by angle-resolved photoemission. Our results show that photoelectron coherence is limited by the crystal corrugation. However, by combining surface morphology measurements of the graphene roughness with angle-resolved photoemission, energy dependent quasiparticle lifetime and bandstructure measurements can be extracted. Our measurements rely on our development of an analytical formulation for relating the crystal corrugation to the photoemission linewidth. Our ARPES measurements show that, despite significant deviation from planarity of the crystal, the electronic structure of exfoliated suspended graphene is nearly that of ideal, undoped graphene; we measure the Dirac point to be within 25 meV of $E_F$ . Further, we show that suspended graphene behaves as a marginal Fermi-liquid, with a quasiparticle lifetime which scales as $(E - E_F)^{-1}$; comparison with other graphene and graphite data is discussed.