Quasi-Flat Plasmonic Bands in Twisted Bilayer Graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Optics

Background:

• Twisted bilayer graphene exhibits unique electronic properties due to interlayer coupling.
• Understanding collective excitations is crucial for novel electronic and optical applications.

Purpose of the Study:

• Investigate the charge susceptibility of twisted bilayer graphene.
• Identify and characterize collective excitonic modes in the Dirac cone regime.
• Explore potential applications of these findings.

Main Methods:

• Theoretical investigation using the random-phase approximation.
• Analysis of charge susceptibility in the Dirac cone approximation.
• Modeling of loss function as a Fano resonance.

Main Results:

• Weakly Landau damped interband plasmons were identified for twist angles below 2 degrees.
• These collective excitonic modes exhibit nearly constant energy dispersion.
• The loss function is accurately described by a Fano resonance.

Conclusions:

• Excitations arise from the interaction of quasi-localized states with light.
• Predictions are testable via nanoinfrared imaging.
• Potential applications include a "perfect" lens without left-handed materials.