Magnetic and electric Mie-exciton polaritons in silicon nanodisks

Light-matter interactions at the nanoscale constitute a fundamental ingredient for engineering applications in nanophotonics and quantum optics. In this regard, Mie resonances supported by high-refractive index dielectric nanoparticles have recently attracted interest, due to their lower losses and better control over the scattering patterns compared to their plasmonic counterparts. The emergence of several resonances in high-refractive index dielectric nanoparticles results in an overall high complexity, where the electric and magnetic dipoles can show a significant spectral overlap, especially at optical frequencies, thus hindering possible light-matter coupling mechanisms arising in the optical spectrum. This behavior can be properly adjusted by using non-spherical geometries, an approach that has already been successfully exploited to tune directional scattering from dielectric nanoresonators. Here, by using cylindrical nanoparticles, we show, experimentally and theoretically, the emergence of peak splitting for both magnetic and electric dipole resonances of individual silicon nanodisks coupled to a J-aggregated organic semiconductor. In the two cases, we find that the different character of the involved resonances leads to different light-matter coupling regimes. Crucially, our results show that the observed energy splittings are of the same order of magnitude as the ones reported using similar plasmonic systems, thereby confirming dielectric nanoparticles as promising alternatives for localized strong coupling studies. The coupling of both the electric and magnetic dipole resonances can offer interesting possibilities for the control of directional light scattering in the strong coupling regime and the dynamic tuning of nanoscale light-matter hybrid states by external fields.