Transport gap engineering by contact geometry in graphene nanoribbons: Experimental and theoretical studies on artificial materials

TL;DR

This study combines microwave emulation experiments and tight-binding calculations to explore how contact geometry influences the transport gap in graphene nanoribbons, revealing conditions for metallic and semiconducting behavior.

Contribution

It demonstrates the significant impact of contact geometry on transport gaps in graphene nanoribbons through combined experimental and theoretical approaches.

Findings

Armchair ribbons of width 3m+2 are metallic; others are semiconducting.

Zigzag ribbons are metallic regardless of width.

Contact attachment to inner atoms induces broad transport gaps.

Abstract

Electron transport in small graphene nanoribbons is studied by microwave emulation experiments and tight-binding calculations. In particular, it is investigated under which conditions a transport gap can be observed. Our experiments provide evidence that armchair ribbons of width $3m+2$ with integer $m$ are metallic and otherwise semiconducting, whereas zigzag ribbons are metallic independent of their width. The contact geometry, defining to which atoms at the ribbon edges the source and drain leads are attached, has strong effects on the transport. If leads are attached only to the inner atoms of zigzag edges, broad transport gaps can be observed in all armchair ribbons as well as in rhomboid-shaped zigzag ribbons. All experimental results agree qualitatively with tight-binding calculations using the nonequilibrium Green's function method.