Disorder-induced gap behavior in graphene nanoribbons

TL;DR

This study investigates how disorder affects the electronic transport gaps in graphene nanoribbons, revealing that the transport gap is linked to disorder strength while the source-drain gap depends on disorder details.

Contribution

The paper provides experimental evidence that distinguishes the effects of disorder strength and details on transport gaps in graphene nanoribbons.

Findings

Transport gap is independent of ribbon length.

Source-drain gap increases with ribbon length.

Annealing reduces the transport gap but not the source-drain gap.

Abstract

We study the transport properties of graphene nanoribbons of standardized 30 nm width and varying lengths. We find that the extent of the gap observed in transport as a function of Fermi energy in these ribbons (the "transport gap") does not have a strong dependence on ribbon length, while the extent of the gap as a function of source-drain voltage (the "source-drain gap") increases with increasing ribbon length. We anneal the ribbons to reduce the amplitude of the disorder potential, and find that the transport gap both shrinks and moves closer to zero gate voltage. In contrast, annealing does not systematically affect the source-drain gap. We conclude that the transport gap reflects the overall strength of the background disorder potential, while the source-drain gap is sensitively dependent on its details. Our results support the model that transport in graphene nanoribbons occurs through quantum dots forming along the ribbon due to a disorder potential induced by charged impurities.