Generation of bound states in the continuum via geometric stretching of plasmonic moiré superlattices

“Bound states in the continuum” (BIC) describes an ideal physical system exhibiting zero radiative loss, which enables an infinitely high-quality factor and corresponding infinite lifetime of the resonance. Currently, many studies have successfully achieved BIC in lossless dielectric systems. Realizing BICs in lossy plasmonic systems remains a challenge. In this article, utilizing the tunability by the twisted angles as well as the versatile light wave manipulation within the moiré superlattices, we theoretically and numerically explore the achievement of BIC through geometric stretching of plasmonic moiré superlattices. The topological geometry properties of the stretched plasmonic moiré superlattice are modified, enabling the generation of two distinct types of BIC: Friedrich-Wintgen BIC and symmetry-protected BIC. Furthermore, a quasi-BIC refractive index sensor that maintains a high Q-factor is demonstrated by exhibiting high sensitivity to refractive index changes. The realization of BICs in the plasmonic moiré superlattices offers potential applications in biomedical sensing, optical communications, and light wave manipulation.