Supercavity mode in a single metallic resonator

Bound states in the continuum are exotic nonradiating modes with very high quality factors enabling enhanced wave-matter interactions. While they typically require array-type of systems, versions of such states have been reported in single dielectric resonators, giving rise to suppressed scattering states termed supercavity modes. In this work, we experimentally demonstrate a supercavity mode in an all-metallic resonator open for probing by free-space microwaves. Our design exploits careful tailoring of the boundaries around the resonator, which supports an octupole mode fostering a significant increase in the quality factor. The main advantage of the resonator is its simplicity and robustness, and it may be utilized as a stand-alone unit for energy harvesting and sensing or as an element for advanced functional material designs.