Termination-Driven Control over BIC Q-Factors and Frequencies in Plasmonic Double Net Metamaterials

TL;DR

This paper investigates how termination design in plasmonic double net metamaterials influences their resonant frequencies and quality factors, revealing new insights into mode control and challenging homogenization models.

Contribution

It introduces a novel scattering approach incorporating evanescent bulk states to better understand and engineer mode properties in terminated plasmonic networks.

Findings

Termination type critically affects mode frequency and Q-factor.

Homogenization models fail to accurately predict the physics of these structures.

New engineering principles enable tailored mode control for applications like coherent light generation.

Abstract

Interlaced metallic wire meshes are 3D metamaterials consisting of two intertwined metallic networks. These plasmonic double nets give rise to otherwise unobserved longitudinal, weakly dispersive and broadband electron acoustic modes from the effective plasma frequency of the double net down to arbitrarily low frequencies. These modes have recently been shown to generate confined slab modes with extremely long lifetimes (high quality factors), so-called quasi-bound states in the continuum. This work reveals the central role of the double net termination in determining the mode's resonant frequency and quality factor. We compare two limiting cases, a tennis net termination recently studied experimentally by others and a protruding column array with a much lower quality factor, as demonstrated by microwave transmission experiments and full-wave simulations. Our work thus vividly demonstrates the failure of a homogenisation approach to explain and quantify the physics of terminated plasmonic network materials. We introduce a new approach, in which additional evanescent bulk states are included in the scattering problem, yielding a qualitative understanding of the slab's optical response. The resulting engineering principles pave the way for the design and exploitation of these materials for applications such as coherent light generation.