Optical Magnetic Multipolar Resonances in Large Dynamic Metamolecules

Abstract

Dynamic metamolecules (DMMs) are composed of a hydrogel dielectric core surrounded by randomly packed plasmonic nanobeads. The optical properties of DMMs can be tuned by controlling their core diameter using temperature variations. We have recently shown that DMMs display strong optical magnetism, including magnetic dipole and magnetic quadrupole resonances, offering significant potential for novel applications. Here, we use a T-matrix approach to characterize the magnetic multipole resonance modes of model metamolecules and explore their presence in experimental data. We show that high-order multipole resonances become prominent as the nanobead or the overall structure size is increased and when the interbead gap is decreased. In this limit, mode mixing among high-order magnetic multipole modes also becomes significant, particularly in the directional scattering spectra. We discuss trends in magnetic scattering observed in both experiments and simulations and provide suggestions for the experimental design and verification of high-order optical magnetic resonances using forward and backward scattering measurements. In addition, we show that the angular scattering of higher-order magnetic modes can display Fano-like interference patterns, which should also be experimentally detectable.