Bound states in the continuum in plasmonic structures

In recent years, we observe a growing interest in the study of resonant effects in subwavelength photonic systems underpinned by the physics of bound states in the continuum. Usually, the resonant effects are associated with low loss dielectric structures such as metasurfaces. However, bound states in the continuum 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. However, such approach provides novel tools for creating sharp resonances in plasmonic nanostructures. Here, we summarize the recent progress in both theoretical and experimental studies of plasmonic bound states in the continuum 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 analogs of electromagnetically induced transparency, and Tamm plasmon polaritons can be associated closely with the physics of bound states in the continuum. In addition, we discuss the future opportunities for the study of high-Q resonant plasmonic systems with bound states in the continuum and highlight related areas where they can contribute to novel physics and important applications.