Electronic transport properties of graphene nanoribbons

TL;DR

This paper reviews the electronic and transport properties of graphene nanoribbons, emphasizing how edge shapes and impurity types influence conduction, revealing unique behaviors in zigzag and armchair configurations.

Contribution

It provides a comparative analysis of zigzag and armchair graphene nanoribbons, highlighting the effects of edge structure and impurity range on their electronic transport properties.

Findings

Zigzag edges support a perfectly conducting channel with long-range impurities.

Armchair edges exhibit nearly perfect conduction despite lack of valley separation.

Symmetry class of disordered zigzag ribbons depends on impurity range.

Abstract

We will present brief overview on the electronic and transport properties of graphene nanoribbons focusing on the effect of edge shapes and impurity scattering. The low-energy electronic states of graphene have two non-equivalent massless Dirac spectrum. The relative distance between these two Dirac points in the momentum space and edge states due to the existence of the zigzag type graphene edges are decisive to the electronic and transport properties of graphene nanoribbons. In graphene nanoribbons with zigzag edges, two valleys related to each Dirac spectrum are well separated in momentum space. The propagating modes in each valley contain a single chiral mode originating from a partially flat band at band center. This feature gives rise to a perfectly conducting channel in the disordered system, if the impurity scattering does not connect the two valleys, i.e. for long-range impurity potentials. On the other hand, the low-energy spectrum of graphene nanoribbons with armchair edges is described as the superposition of two non-equivalent Dirac points of graphene. In spite of the lack of well-separated two valley structures, the single-channel transport subjected to long-ranged impurities is nearly perfectly conducting, where the backward scattering matrix elements in the lowest order vanish as a manifestation of internal phase structures of the wavefunction. Symmetry considerations lead to the classification of disordered zigzag ribbons into the unitary class for long-range impurities, and the orthogonal class for short-range impurities. However, no such crossover occurs in armchair nanoribbons.