Plexcitonic Quasi‐Bound States in the Continuum

Abstract Enhancing light‐matter interactions is fundamental to the advancement of nanophotonics and optoelectronics. Yet, light diffraction on dielectric platforms and energy loss on plasmonic metallic systems present an undesirable trade‐off between coherent energy exchange and incoherent energy damping. Through judicious structural design, both light confinement and energy loss issues could be potentially and simultaneously addressed by creating bound states in the continuum (BICs) where light is ideally decoupled from the radiative continuum. Herein, the authors present a general framework based on the two‐coupled resonances to first conceptualize and then numerically demonstrate a type of quasi‐BICs that can be achieved through the interference between two bare resonance modes and is characterized by the considerably narrowed spectral line shape even on lossy metallic nanostructures. The ubiquity of the proposed framework further allows the paradigm to be extended for the realization of plexcitonic quasi‐BICs on the same metallic systems. Owing to the topological nature, both plasmonic and plexcitonic quasi‐BICs display strong mode robustness against parameters variation, thereby providing an attractive platform to unlock the potential of the coupled plasmon‐exciton systems for manipulation of the photophysical properties of condensed phases.