Plasmonic Bound States in the Continuum in Compact Nanostructures

Optical bound states in the continuum (BICs) have become a unique way to produce the extreme localization and enhancement of light waves, however, it remains challenging to realize them in single-particle systems. This work shows the existence of optical BICs in a compact corrugated metallic cylinder, and quasi-BICs are observed in multiple channels when adjacent grooves have different depths. It is revealed that such BICs are purely plasmonic, resulting from the destructive interference of two localized surface plasmon modes in the nanostructures. Benefiting from the surface plasmon effects, the findings extend optical BICs and the associated physics to subwavelength optics, providing a route to break the diffraction limit and boost light-matter interactions.