Quasi-flat plasmonic bands in twisted bilayer graphene

TL;DR

This paper explores the unique plasmonic properties of twisted bilayer graphene at small twist angles, revealing weakly damped interband plasmons with potential applications in advanced optical devices.

Contribution

It provides the first detailed analysis of charge susceptibility and plasmonic excitations in twisted bilayer graphene within the Dirac cone approximation using RPA.

Findings

Existence of weakly Landau damped interband plasmons at small twist angles

Plasmonic excitations can be described as Fano resonances

Potential for nano-infrared imaging and perfect lens applications

Abstract

The charge susceptibility of twisted bilayer graphene is investigated in the Dirac cone, respectively random-phase approximation. For small enough twist angles $\theta\lesssim 2^\circ$ we find weakly Landau damped interband plasmons, i.~e., collective excitonic modes which exist in the undoped material, with an almost constant energy dispersion. In this regime, the loss function can be described as a Fano resonance and we argue that these excitations arise from the interaction of quasi-localised states with the incident light field. These predictions can be tested by nano-infrared imaging and possible applications include a "perfect" lens without the need of left-handed materials.