A plasmon-induced current loop in gold semi-shells

We perform a computational investigation of the optical properties of nanoscale gold 'semi-shells' and show how additional plasmon resonances develop as the shape is successively mutated from 'nanoshell' to 'nano-cup', 'half-shell' and finally to 'nano-cap'. The effects of aspect ratio, surface roughness and cut-off height are explored. Of special interest is a new longitudinal resonance that generates an electric current loop. We predict that this will induce an orthogonal magnetic component that will sum with the magnetic component of incident light at certain orientations. Exploitation of this phenomenon in an ordered array of semi-shells may produce anomalous optical effects due to an altered magnetic permeability.