Anapole States and Toroidal Resonances Realized in Simple Gold Nanoplate‐on‐Mirror Structures

Abstract

Abstract Optical anapoles are often realized with high‐refractive‐index dielectric nanoparticles or metallic metamaterials with complex geometries. In this work, anapole states and plasmon‐induced toroidal resonances are observed on a simple plasmonic configuration, which is made of individual Au nanoplates supported on Au films. The nanoplate and the film are separated by a precisely sized dielectric spacer layer. Both the fundamental and higher‐order anapole states are experimentally observed in the far‐field scattering measurements and confirmed by electrodynamic simulations. The geometrical parameters of the nanoplate‐on‐mirror cavity are found to play sensitive and significant roles in altering the anapole excitation, which allows the resonant dip to be tailored from the visible to near‐infrared region. In addition, magnetic plasmon resonance is also realized in the nanoplate‐on‐mirror system when the thickness of the spacer layer is increased. These results provide new insights for engineering simple plasmonic nanostructures with nontrivial yet controllable responses and developing anapole‐based plasmonic applications.