Effect of edge reconstruction and electron-electron interactions on quantum transport in graphene nanoribbons

TL;DR

This study investigates how edge reconstruction and electron interactions affect quantum transport in graphene nanoribbons, revealing defect-induced backscattering, transport gaps, and the nuanced role of electron-electron interactions.

Contribution

It combines density functional theory with tight-binding models to analyze defect effects on conductance, providing new insights into transport gaps and defect interactions in graphene nanoribbons.

Findings

Transport gap scales inversely with ribbon width.

Stone-Wales defects cause the largest transport gaps.

Electron interactions can reduce backscattering and enhance conductance.

Abstract

We present numerical studies of conduction in graphene nanoribbons with reconstructed edges based on the standard tight-binding model of the graphene and the extended Huckel model of the reconstructed defects. We performed atomic geometry relaxation of individual defects using density functional theory and then explicitly calculated the tight-binding parameters used to model electron transport in graphene with reconstructed edges. The calculated conductances reveal strong backscattering and electron-hole asymmetry depending on the edge and defect type. This is related to an additional defect-induced band whose wave function is poorly matched to the propagating states of the pristine ribbon. We find a transport gap to open near the Dirac point and to scale inversely with the ribbon width, similarly to what has been observed in experiments. We predict the largest transport gap to occur for armchair edges with Stone-Wales defects, while heptagon and pentagon defects cause about equal backscattering for electrons and holes, respectively. Choosing the heptagon defect as an example, we show that although electron interactions in the Hartree approximation cause accumulation of charge carriers on the defects, surprisingly, their effect on transport is to reduce carrier backscattering by the defects and thus to enhance the conductance.