Plasmons Driven by Single Electrons in Graphene Nanoislands

TL;DR

This paper demonstrates that adding single electrons to graphene nanoislands can activate and dramatically tune infrared plasmons, revealing quantum effects and high sensitivity useful for nano-optoelectronics.

Contribution

It uncovers the quantum-driven plasmon activation and tuning in graphene nanoislands caused by single-electron addition, contrasting classical predictions.

Findings

Single electrons activate infrared plasmons in graphene nanoislands.

Plasmon frequencies shift significantly with each added electron.

Edge structure critically influences plasmon support and properties.

Abstract

Plasmons produce large confinement and enhancement of light that enable applications as varied as cancer therapy and catalysis. Adding to these appealing properties, graphene has emerged as a robust, electrically tunable material exhibiting plasmons that strongly depend on the density of doping charges. Here we show that adding a single electron to a graphene nanoisland consisting of hundreds or thousands of atoms switches on infrared plasmons that were previously absent from the uncharged structure. Remarkably, the addition of each further electron produces a dramatic frequency shift. Plasmons in these islands are shown to be tunable down to near infrared wavelengths. These phenomena are highly sensitive to carbon edges. Specifically, armchair nanotriangles display sharp plasmons that are associated with intense near-field enhancement, as well as absorption cross-sections exceeding the geometrical area occupied by the graphene. In contrast, zigzag triangles do not support these plasmons. Our conclusions rely on realistic quantum-mechanical calculations, which are in ostensible disagreement with classical electromagnetic simulations, thus revealing the quantum nature of the plasmons. This study shows a high sensitivity of graphene nanoislands to elementary charges, therefore emphasizing their great potential for novel nano-optoelectronics applications.