Hybridization of Localized Surface Phonon Polaritons <i>via</i> Symmetry Breaking in Dolmen Nanostructures

Subdiffractional confinement of light coupled with low optical losses mediated through surface phonons polaritons (SPhPs) in polar dielectric materials such as SiC have enabled infrared based nanophotonic applications. By utilizing a nano-Dolmen architecture, we experimentally and theoretically demonstrate hybridization between localized, sub-diffractional SPhP modes via spatial symmetry breaking. The substrate mediated, extended coupling nature of the vertically oriented monopole leads to gap-tunable symmetric and antisymmetric modes with high quality factors (200-250) and field localization in the coupled oscillator. By theoretical modelling we demonstrate monopolar excitation, otherwise excited so far only by off-normal light, through dipolar nearfields via normal incidence by overcoming the selection rules leading to direct and indirect excitation pathways for monopolar activation in the Dolmen system. Further, in contrast to the plasmonic systems, despite strong coupling the bound continuum states in narrow SPhP modes do not exhibit Fano interference. By controlling nanoscale geometry, spacing and excitation, we are able to obtain highly tunable optical responses resulting in strong phonon polariton hybridization and large near-field enhancements in these high-Q resonators.