Strong optical magnetism and Fano resonances in asymmetric plasmonic metamolecules

We theoretically and experimentally show that a subwavelength plasmonic ring consisting of four gold nanoparticles can support strong artificial magnetism and magnetic-based Fano resonances at optical frequencies. This is achieved through controlled symmetry breaking of the nanoring geometry, which induces tailored interference between electric and magnetic plasmon modes supported by the nanocluster, leading to enhanced optical magnetism and a distinctively sharp Fano response in the scattering spectrum. These results pave the way to building blocks for negative-index metamaterials and novel single-molecule, magnetic-based biosensors.