Unconventional bound states in the continuum from metamaterial induced electron-acoustic plasma waves

TL;DR

This paper introduces a new fundamental mechanism for creating bound states in the continuum in metamaterials, which are robust, resonance-free, and include bulk and topological surface states, advancing photonic and electronic applications.

Contribution

It proposes a generic, resonance-free mechanism for BICs based on double-net metamaterials, enabling robust bulk and topological surface bound states.

Findings

Prediction of two new BIC types: bulk-confined modes and topological surface states.

Demonstration of resonance-free, parameter-tunable BICs in metamaterials.

Identification of the fundamental band in double-net metamaterials as the basis for BICs.

Abstract

Photonic bound states in the continuum are spatially localised modes with infinitely long lifetimes that exist within a radiation continuum at discrete energy levels. These states have been explored in various systems where their emergence is either guaranteed by crystallographic symmetries or due to topological protection. Their appearance at desired energy levels is, however, usually accompanied by non-BIC resonances, from which they cannot be disentangled. Here, we propose a new generic mechanism to realize bound states in the continuum that exist by first principles free of other resonances and are robust upon parameter tuning. The mechanism is based on the fundamental band in double-net metamaterials, which provides vanishing homogenized electromagnetic fields. We predict two new types of bound states in the continuum: i) generic modes confined to the metamaterial bulk, mimicking electronic acoustic waves in a hydrodynamic double plasma, and ii) topological surface bound states in the continuum.