Interfaces Within Graphene Nanoribbons

TL;DR

This paper investigates conductance in graphene nanoribbons with varying geometries, revealing that interfaces and valley degrees of freedom significantly influence electron transport, unlike traditional electron gas waveguides.

Contribution

It demonstrates that graphene nanostructures exhibit unique conductance behaviors due to valley and sublattice effects, differing from classical waveguide expectations.

Findings

Substantial reflection occurs at wide-narrow interfaces.

Conductance in curved nanoribbons is highly sensitive to structural details.

Valley degree of freedom influences conductance suppression.

Abstract

We study the conductance through two types of graphene nanostructures: nanoribbon junctions in which the width changes from wide to narrow, and curved nanoribbons. In the wide-narrow structures, substantial reflection occurs from the wide-narrow interface, in contrast to the behavior of the much studied electron gas waveguides. In the curved nanoribbons, the conductance is very sensitive to details such as whether regions of a semiconducting armchair nanoribbon are included in the curved structure -- such regions strongly suppress the conductance. Surprisingly, this suppression is not due to the band gap of the semiconducting nanoribbon, but is linked to the valley degree of freedom. Though we study these effects in the simplest contexts, they can be expected to occur for more complicated structures, and we show results for rings as well. We conclude that experience from electron gas waveguides does not carry over to graphene nanostructures. The interior interfaces causing extra scattering result from the extra effective degrees of freedom of the graphene structure, namely the valley and sublattice pseudospins.