Contact conductance between graphene and quantum wires

TL;DR

This paper theoretically investigates how the contact conductance between graphene and quantum wires varies with coupling configurations, revealing effects of chirality, sublattice structure, and lead separation on conductance behavior.

Contribution

It provides a detailed analysis of the dependence of contact conductance on coupling configurations and distance, highlighting the role of graphene's chirality and sublattice structure.

Findings

Contact conductance vanishes at the Dirac point when each wire couples to one carbon atom in the same sublattice.

Conductance decays rapidly as the distance between leads increases.

In weak coupling, conductance is proportional to the square of contact area and inversely proportional to the square of lead separation.

Abstract

The contact conductance between graphene and two quantum wires which serve as the leads to connect graphene and electron reservoirs is theoretically studied. Our investigation indicates that the contact conductance depends sensitively on the graphene-lead coupling configuration. When each quantum wire couples solely to one carbon atom, the contact conductance vanishes at the Dirac point if the two carbon atoms coupling to the two leads belong to the same sublattice of graphene. We find that such a feature arises from the chirality of the Dirac electron in graphene. Such a chirality associated with conductance zero disappears when a quantum wire couples to multiple carbon atoms. The general result irrelevant to the coupling configuration is that the contact conductance decays rapidly with the increase of the distance between the two leads. In addition, in the weak graphene-lead coupling limit, when the distance between the two leads is much larger than the size of the graphene-lead contact areas and the incident electron energy is close to the Dirac point, the contact conductance is proportional to the square of the product of the two graphene-lead contact areas, and inversely proportional to the square of the distance between the two leads.