Dark to Bright Mode Conversion on Dipolar Nanoantennas: A Symmetry-Breaking Approach

The excitation of plasmonic dark modes via a radiative channel is a phenomenon strongly hindered in the subwavelength regime. Recently, for achieving this purpose it has been proposed to exploit near-field interactions between radiating (bright) modes and lossless dark modes. However, this approach unveils challenging difficulties related to the excitation of dark modes through the near-field coupling with a bright mode. Here, it is experimentally and numerically shown how symmetry breaking applied to a nanoantenna dimer can conversely induce the excitation of plasmonic resonances, which play a key role for the dark modes' activation in more complex nanoassemblies. On the basis of this study, a T-shaped nanoantenna trimer has been introduced as an elemental unit for the energy transfer between bright and dark modes in plasmonic nanostructures. Finally, we implemented an analytical perturbative model to further investigate the plasmonic hybridization of subwavelength systems.