Optical Monitoring of the Magnetoelectric Coupling in Individual Plasmonic Scatterers

Abstract

Engineering the shape of metallic nanostructures is of crucial interest to tailor the electric and magnetic fields at a deep subwavelength scale. Individual nanoscatterers behave as optical atoms with strong electric and magnetic responses that can be tuned via the composition and the shape of the nano-object. U-shaped scatterers are assumed to exhibit strong magnetoelectric coupling, yielding local chiral fields. However, these magneto-optical couplings have never been measured at the scale of a single meta-atom. In this paper, we report transmission measurements performed on individual U-shaped metallic scatterers using different linear polarization conditions. A point multipole model, with modes up to the electric quadrupole, including magnetoelectric coupling, provides an excellent description of the polarization-dependent optical response of the single scatterer for different directions of propagation. The comparison of this model with the optical measurements allows quantifying the magnitude of the different multipoles and more importantly of the magnetoelectric coupling over the visible and near-infrared spectrum.