Toroidal Dipole Excitation in Metamaterial Perfect Absorber Consisting of Dielectric Nanodisks Quadrumer Clusters and Spacer on Metal Substrate

We proposed an infrared narrowband metamaterial perfect absorber (MPA) which is induced by toroidal dipole resonance in a dielectric-metal hybrid system. The MPA is composed of amorphous-silicon (a-Si) nanodisk quadrumer clusters, dielectric spacer, and Au substrate, where the dielectric spacer is inserted between Si disk quadrumer and Au substrate. Near field distribution and multipole decomposition of far-field, scattering powers show that toroidal dipole mode is formed by opposite phase magnetic dipoles in neighboring Si nanodisks. The effects of geometric and material parameters on absorption characteristics were explored. The sensing performance of the MPA was also evaluated. The proposed MPA has potential applications in air sensing applications. Since the nanodisc quadrumer of the MPA retains C_4v symmetry, perfect absorption band is polarization independent. Furthermore, the absorption quality factor of the hybrid dielectric-metal hybrid absorber is higher than that of all-metal perfect absorbers, thanks to the low loss feature of the dielectric resonator.