Tunability of Subradiant Dipolar and Fano-Type Plasmon Resonances in Metallic Ring/Disk Cavities: Implications for Nanoscale Optical Sensing

Plasmonic nanocavities consisting of the concentric arrangement of a disk and a ring sustain both subradiant and superradiant dipolar plasmon modes with large associated field enhancements and high refractive index sensitivities. In structures with broken symmetry, additionally a highly tunable Fano interference feature appears, which can be explained with a simple analytical harmonic oscillator model. The spectral tunability of these resonances from the visible to the mid-infrared is investigated, highlighting a potential for applications in surface enhanced spectroscopies.