Coherent transport in graphene nanoconstrictions

TL;DR

This paper investigates how nanoconstrictions in graphene ribbons affect coherent electronic transport, revealing robustness of bulk current and localized states near the Fermi energy, with implications for quantum dot formation.

Contribution

It provides a detailed analysis of transport properties in graphene nanoconstrictions, highlighting the effects of geometry and defects on conductance and localized states.

Findings

Bulk current is robust against constriction geometries and edge defects.

Single-atom removal alters the conductance staircase.

Localized states can form in wedge-shaped constrictions near the Fermi energy.

Abstract

We study the effect of a structural nanoconstriction on the coherent transport properties of otherwise ideal zig-zag-edged infinitely long graphene ribbons. The electronic structure is calculated with the standard one-orbital tight-binding model and the linear conductance is obtained using the Landauer formula. We find that, since the zero-bias current is carried in the bulk of the ribbon, this is very robust with respect to a variety of constriction geometries and edge defects. In contrast, the curve of zero-bias conductance versus gate voltage departs from the $(2n+1) e^2/h$ staircase of the ideal case as soon as a single atom is removed from the sample. We also find that wedge-shaped constrictions can present non-conducting states fully localized in the constriction close to the Fermi energy. The interest of these localized states in regards the formation of quantum dots in graphene is discussed.