Electronic confinement in quantum dots of twisted bilayer graphene

TL;DR

This paper presents a novel method to create and verify quantum dots in twisted bilayer graphene, revealing unique electronic state modifications due to the twist angle and interlayer coupling variations.

Contribution

It introduces a general fabrication approach for twisted bilayer graphene quantum dots and uncovers their impact on electronic states near van Hove singularities.

Findings

Successful fabrication of TBG quantum dots with nanoscale p-n junctions.

Verification of Dirac fermion confinement via whispering-gallery modes.

Observation of strong modifications in electronic states near van Hove singularities.

Abstract

Electronic properties of quantum dots (QDs) depend sensitively on their parent materials. Therefore, confined electronic states in graphene QDs (GQDs) of monolayer and Bernal-stacked bilayer graphene are quite different. Twisted bilayer graphene (TBG) is distinct from monolayer and Bernal-stacked bilayer graphene because of the new degree of freedom: twist angle. In the past few years, numerous efforts have been made to realize the GQDs of monolayer and Bernal-stacked bilayer graphene and achieved great success. Thus far, however, strategies for realizing GQDs of TBG have been elusive. Here, we demonstrate a general approach for fabricating stationary GQDs of TBG by introducing nanoscale p-n junctions with sharp boundaries in the TBG. We verify the confinement of low-energy massless Dirac fermions via whispering-gallery modes in the GQDs of TBG. Unexpectedly, electronic states around van Hove singularities of the TBG are also strongly modified around the GQDs. Such a feature has never been reported and is attributed to spatial variation of the interlayer coupling in the TBG induced by the GQDs.