Non-radiating excitations, vector potential waves and toroidal metamaterials

A long chase for the elusive dynamic toroidal moments has been recently concluded by detecting a spectral signature of the toroidal dipolar resonance in the response of a specially designed electromagnetic metamaterial [1]. This observation brings up a new interest to the prediction made by Afanasiev and Stepanovsky in 1994 that a combination of oscillating toroidal and conventional electric dipoles forms a non-trivial non-radiating electromagnetic system producing gauge-irreducible waves of vector potential in absence of electric and magnetic fields [2]. Here we report the observation of extremely narrow transmission resonances in toroidal void metamaterials that result from the interference of its electric and toroidal dipolar response thus indicating the existence of such non-radiating system. Our results provide new evidence for the discussion on independent physical significance of vector-potential and its role as an independent information carrier.