Confining graphene plasmons to the ultimate limit

TL;DR

This paper investigates the extreme confinement of graphene plasmons near metal gates, deriving exact dispersion and lifetime results, revealing highly confined, low-damping acoustic plasmons with potential for advanced nanophotonic applications.

Contribution

It provides the first exact analysis of graphene plasmons on metal substrates considering nonlocal effects, demonstrating enhanced confinement and weak damping in this hybrid system.

Findings

Graphene plasmons become acoustic and highly confined near metal gates.

Landau damping remains weak, with quality factors over 100.

The dispersion approaches the intraband particle-hole continuum boundary.

Abstract

Graphene plasmons have recently attracted a great deal of attention because of their tunability, long lifetime, and high degree of field confinement in the vertical direction. Nearby metal gates have been shown to modify the graphene plasmon dispersion and further confine their electric field. We study the plasmons of a graphene sheet deposited on a metal, in the regime in which metal bands do not hybridize with massless Dirac fermion bands. We derive exact results for the dispersion and lifetime of the plasmons of such hybrid system, taking into account metal nonlocalities. The graphene plasmon dispersion is found to be acoustic and pushed down in energy towards the upper boundary of the intraband graphene particle-hole continuum, thereby strongly enhancing the vertical confinement of these excitations. Landau damping of such acoustic plasmons due to particle-hole excitations in the metal gate is found to be surprisingly weak, with quality factors exceeding $Q = 10^{2}$.