Exploring multifrequency bound states in the continuum in square-root topological circuits

Bound states in the continuum (BICs) have attracted significant attention due to their intriguing properties. The introduction of square-root topology often leads to multifrequency topological bound states, enhancing the richness of the system behavior. In this study, we construct a square-root topological circuit hosting topological bound states in multi-frequency gaps based on connected double Su-Schrieffer-Heeger chains. By simple adjustments, the double chains can be decoupled, transitioning into square-root topological bound states in the continuum circuit (STBICs). Experimental validations are conducted to confirm the coexistence of both topological and trivial bound states in these systems. Furthermore, we demonstrate robustness against perturbations, providing strong evidence supporting the topological protection of BICs. Our research bridges the gap between square-root topology and BICs, resulting in rich topological properties and offering insight into the potential applications of square-root topological BICs circuits.