Bound states in the continuum in plasmonic structures

In recent years, increasing attention has been paid to resonant effects in subwavelength photonic systems governed by the physics of bound states in the continuum (BIC). Usually, the resonant effects are associated with low-loss dielectric structures such as metasurfaces. However, BIC is a general wave phenomenon that should be observed in many different systems, including the metal-dielectric structures supporting surface plasmon polaritons, where optical resonances are hindered by losses. This concept provides novel tools for creating sharp resonances in plasmonic nanostructures. Here, we summarize the recent progress in both theoretical and experimental studies of plasmonic BIC with a particular focus on novel properties and applications such as lasing, sensing, and nonlinear properties. In particular, we reveal that plasmonic surface lattice resonances, a metamaterial analog of electromagnetically induced transparency, and Tamm plasmon polaritons can be closely associated with the physics of BIC. In addition, we discuss the future opportunities for the study of high-resonant plasmonic systems with BIC and highlight related areas where they can contribute to novel physics and important applications.