Plasmonic properties of asymmetric disk@nanorings

This study investigates the plasmonic behavior of an asymmetrically positioned nanodisk within a nanoring, revealing the activation of four distinct plasmonic modes within the wavelength range of 200- 2000 nm. By varying the asymmetry parameter, the distance between the centers of the nanodisk and nanoring, we observe remarkable sensitivity. We employ a straightforward model based on binary transformation in complex coordinates to delve into the extraordinary sensitivity of this system. Absorption cross-section analysis shows a progressive blue shift in three plasmonic bands with increasing asymmetry, while the fourth band, displaying a Fano-like resonance, remains stable. Notably, the first plasmonic mode exhibits an exceptional electric field enhancement factor of 71.5, generating an intense hotspot due to charge proximity in the nanodisk-nanoring gap. These results suggest that nanodisks integrated within nanorings offer a promising pathway for optimizing optical nanosensors.