Probing the magnetism of topological end-states in 5-armchair graphene nanoribbons

TL;DR

This study investigates the electronic and magnetic properties of 5-armchair graphene nanoribbons, revealing their topological end states, length-dependent behavior, and magnetic character through combined experimental and theoretical approaches.

Contribution

It provides new insights into the topological nature and magnetic properties of end states in ultra-narrow graphene nanoribbons, supported by experimental and theoretical analysis.

Findings

End states are topologically protected and localized at zig-zag termini.

Length influences the spin state of the end states, transitioning from spin-split to closed-shell.

Magnetic character of end states confirmed via transport measurements.

Abstract

We extensively characterize the electronic structure of ultra-narrow graphene nanoribbons (GNRs) with armchair edges and zig-zag termini that have 5 carbon atoms across their width (5-AGNRs), as synthesised on Au(111). Scanning tunnelling spectroscopy measurements on the ribbons, recorded on both the metallic substrate and a decoupling NaCl layer, show well-defined dispersive bands and in-gap states. In combination with theoretical calculations, we show how these in-gap states are topological in nature and localised at the zig-zag termini of the nanoribbons. Besides rationalising the driving force behind the topological class selection of 5-AGNRs, we also uncover the length-dependent behaviour of these end states which transition from singly occupied spin-split states to a closed-shell form as the ribbons become shorter. Finally, we demonstrate the magnetic character of the end states via transport experiments in a model two-terminal device structure in which the ribbons are suspended between the scanning probe and the substrate that both act as leads.