Topology induced anomalous plasmon modes in metallic Möbius nanorings

摘要

We report on the theoretical investigation of plasmonic resonances in metallic Mobius nanorings. Half-integer numbers of resonant modes are observed due to the presence of an extra phase pi provided by the topology of the Mobius nanostrip. Anomalous plasmon modes located at the non-orientable surface of the Mobius nanoring break the symmetry that exist in conventional ring cavities, thus enable far-field excitation and emission as bright modes. The far-field resonant wavelength as well as the feature of half-integer mode numbers is constant to the change of charge distribution on the Mobius nanoring due to the topology of Mobius ring. Owing to the ultra-small mode volume induced by the remaining dark feature, an extremely high sensitivity as well as a remarkable figure of merit is obtained in our numerical calculations for sensing performance. The topological metallic nanostructure provides a novel platform for the investigation of localized surface plasmon modes exhibiting unique phenomena for potential plasmonic applications.