Giant edge state splitting at atomically precise zigzag edges

TL;DR

This study demonstrates that atomically precise zigzag edges in graphene nanoribbons exhibit a large energy splitting of localized edge states, primarily due to electron-electron interactions, confirmed by experimental and theoretical methods.

Contribution

The paper provides direct experimental evidence of large edge state splitting in atomically precise graphene nanoribbons, highlighting the role of electron-electron interactions.

Findings

Large energy splitting of 1.9 eV observed in edge states

Decoupling from substrate preserves intrinsic edge states

Agreement with ab initio many-body calculations

Abstract

Zigzag edges of graphene nanostructures host localized electronic states that are predicted to be spin-polarized. However, these edge states are highly susceptible to edge roughness and interaction with a supporting substrate, complicating the study of their intrinsic electronic and magnetic structure. Here, we focus on atomically precise graphene nanoribbons whose two short zigzag edges host exactly one localized electron each. Using the tip of a scanning tunneling microscope, the graphene nanoribbons are transferred from the metallic growth substrate onto insulating islands of NaCl in order to decouple their electronic structure from the metal. The absence of charge transfer and hybridization with the substrate is confirmed by scanning tunneling spectroscopy (STS), which reveals a pair of occupied / unoccupied edge states. Their large energy splitting of 1.9 eV is in accordance with ab initio many-body perturbation theory calculations and reflects the dominant role of electron-electron interactions in these localized states.