Design and experimental investigation of a chiral plasmonic nanotaper

The phenomena of coupling between light and surface plasmon polaritons requires specific momentum matching conditions. In the case of a single scattering object on a metallic surface, like a nanoparticle or a nanohole, the coupling between a broadband effect, i.e. scattering, and a discrete one such as surface plasmon excitation, leads to Fano-like plasmonic resonance line-shapes. The necessary phase matching requirements can be used to engineer the light-plasmon coupling and to achieve a directional plasmonic excitation. Here we investigate this effect by using a chiral nanotip to excite surface plasmons with a strong spin-dependent azimuthal variation. This effect can be described by a Fano-like interference with a complex coupling factor that can be modified thanks to a symmetry breaking nanostructure.