Dielectric screening and plasmons in AA-stacked bilayer graphene

TL;DR

This paper investigates the unique plasmonic and screening properties of AA-stacked bilayer graphene, revealing that it supports coherent plasmons even without doping and that external electric fields can tune their dispersion.

Contribution

It demonstrates that AA-stacked bilayer graphene hosts undamped plasmons without doping and shows how gate voltages can modulate their dispersion, a novel finding compared to other graphene stackings.

Findings

Coherent plasmons exist in AA-stacked bilayer graphene without doping.

The low energy dispersion relation remains unchanged unless doping exceeds inter-layer hopping energy.

External electric fields can tune the plasmon dispersion.

Abstract

The screening properties and collective excitations (plasmons) in AA-stacked bilayer graphene are studied within the random phase approximation (RPA). Whereas long lived plasmons in single layer graphene and in AB-stacked bilayer graphene can exist only in doped samples, we find that coherent plasmons can disperse in AA-stacked bilayer graphene {\it even in the absence of doping}. Moreover, we show that the characteristic low energy dispersion relation is unaffected by changes in the number of carriers, unless the chemical potential of the doped sample exceeds the inter-layer hopping energy. We further consider the effect of an external electric field applied perpendicular to the layers, and show how the dispersion of the modes can be tuned by the application of a gate voltage.