Quasi-Flat Plasmonic Bands in Twisted Bilayer Graphene.

The charge susceptibility of twisted bilayer graphene is investigated in the Dirac cone, respectively, random-phase approximation. For small enough twist angles θ ≲ 2°, we find weakly Landau damped interband plasmons, that is, collective excitonic modes that 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-localized states with the incident light field. These predictions can be tested by nanoinfrared imaging and possible applications include a "perfect" lens without the need of left-handed materials.