Magnetically controllable and topologically protected bound states in the continuum in photonic crystals

In this study, we theoretically introduce magnetically controllable, topologically protected bound states in the continuum (BICs) arising from a two-dimensional photonic crystal composed of yttrium iron garnet. The system’s electromagnetic properties change markedly based on the magnetization state of the YIG. Different magnetization directions of the YIG disks induce chiral edge states in the photonic crystal, enabling the formation of BICs. Our findings show that magnetization can be used to control BICs, presenting new possibilities for designing robust, adaptable optical devices. This work opens up future possibilities for exploring and utilizing magnetically tunable photonic structures in advanced optical technologies.