Classical and Quantum Plasmonics in Graphene Nanodisks: the Role of Edge States

TL;DR

This paper investigates how edge states in doped graphene nanodisks influence quantum plasmonic behavior, revealing their impact on resonance shifts, broadening, and absorption efficiency through microscopic calculations and simplified models.

Contribution

It introduces a new term in the conductivity accounting for edge-bulk coupling and develops models to describe plasmonics in ultrasmall graphene nanodisks with edge states.

Findings

Edge states cause red-shift and broadening of plasmon resonance.

Edge states significantly affect absorption efficiency.

Simplified hydrodynamical models can semi-quantitatively describe the phenomena.

Abstract

Edge states are ubiquitous for many condensed matter systems with multicomponent wave functions. For example, edge states play a crucial role in transport in zigzag graphene nanoribbons. Here, we report microscopic calculations of quantum plasmonics in doped graphene nanodisks with zigzag edges. We express the nanodisk conductivity $\sigma(\omega)$ as a sum of the conventional bulk conductivity $\sigma_{\scriptscriptstyle\text{B}}(\omega)$, and a novel term $\sigma_{\scriptscriptstyle\text{E}}(\omega)$, corresponding to a coupling between the edge and bulk states. We show that the edge states give rise to a red-shift and broadening of the plasmon resonance, and that they often significantly impact the absorption efficiency. We further develop simplified models, incorporating nonlocal response within a hydrodynamical approach, which allow a semiquantitative description of plasmonics in the ultrasmall size regime. However, the polarization dependence is only given by fully microscopic models. The approach developed here should have many applications in other systems supporting edge states.