Nonlocal effects in plasmonic metasurfaces with almost touching surfaces

TL;DR

This paper investigates nonlocal optical effects in plasmonic metasurfaces with near-touching surfaces, revealing how these effects influence resonance behavior and cannot be ignored in ultra-thin structures.

Contribution

The study introduces an analytical approach using transformation optics to model nonlocal effects in near-singular plasmonic metasurfaces, advancing understanding of their optical responses.

Findings

Nonlocal effects cause a blueshift of resonance peaks.

Reduced density of states due to nonlocal effects.

Analytical modeling applicable to various ultra-thin metasurfaces.

Abstract

Geometrical singularities in plasmonic metasurfaces have recently been proposed for the enhancement of light-matter interactions, owing to their broadband light-harvesting properties and extreme plasmon confinement. However, the large plasmon momenta thus achieved lead to failure of local descriptions of the optical response of metals. Here we study a class of metasurfaces consisting of a periodic metal slab with a smooth modulation of its thickness. When the thinnest part shrinks, the two surfaces almost touch, forming a near-singular point. Using transformation optics, we show analytically how nonlocal effects, such as a blueshift of the resonance peaks and a reduced density of states, become important and cannot be ignored in this singular regime. The method developed in this paper is very general and can be used to model a variety of metasurfaces, providing valuable insight in the current context of ultra-thin plasmonic structures.