Material induced bianisotropy of hybrid nanostructures: From a single meta-atom resonance to metasurfaces with trapped modes

Abstract

The optical properties of Janus-type hybrid silicon-gold nanocylinders are theoretically studied. We show that the inhomogeneity of the internal material in these particles causes a strong bianisotropic response. Their lack of inversion symmetry formally determines the bianisotropic response of hybrid nanocylinders. We demonstrate a method for obtaining in advance information on nonzero components of the dipole polarizability tensor of hybrid particles by analyzing the relationship between their symmetry properties and the multipole composition of their eigenmodes. The spectral response of metasurfaces composed of a periodic arrangement of such particles can feature strong resonances associated with multipole coupling and the excitation of quasibound states in the continuum (quasi-BICs). Using the resonant bianisotropic properties of the hybrid particles and the ability to tune the quasi-BICs (trapped modes) to a predetermined wavelength by choosing the metasurface period, we demonstrate the excitation of electric and magnetic types of quasi-BICs in the infrared region. The ability to switch between these types of quasi-BICs by changing the incident light polarization is discussed. We also demonstrate that, unlike purely dielectric metasurfaces, the excitation of the quasi-BICs in hybrid metasurfaces leads to a resonant absorption of light. Published by the American Physical Society 2025