Anomalous Enhancement of the Boltzmann Conductivity in Disordered Zigzag Graphene Nanoribbons

TL;DR

This paper investigates how weak intervalley scattering in disordered zigzag graphene nanoribbons leads to an unexpected enhancement of conductivity, approaching a perfectly conducting state even in the incoherent regime.

Contribution

It demonstrates that in disordered zigzag graphene nanoribbons, weak intervalley scattering causes anomalous conductivity enhancement, approaching perfect conduction.

Findings

Conductivity approaches unity with increasing ribbon length when intervalley scattering is absent.

Anomalous valley polarization of electron density occurs under electric fields.

Weak intervalley scattering stabilizes a nearly perfectly conducting state.

Abstract

We study the conductivity of disordered zigzag graphene nanoribbons in the incoherent regime by using the Boltzmann equation approach. The band structure of zigzag nanoribbons contains two energy valleys, and each valley has an excess one-way channel. The crucial point is that the numbers of conducting channels for two propagating directions are imbalanced in each valley due to the presence of an excess one-way channel. It was pointed out that as a consequence of this imbalance, a perfectly conducting channel is stabilized in the coherent regime if intervalley scattering is absent. We show that even in the incoherent regime, the conductivity is anomalously enhanced if intervalley scattering is very weak. Particularly, in the limit of no intervalley scattering, the dimensionless conductance approaches to unity with increasing ribbon length as if there exists a perfectly conducting channel. We also show that anomalous valley polarization of electron density appears in the presence of an electric field.