Coupling effects in plasmonic nanoparticle arrays: The weak and the strong coupling regime and the effects of spin-orbit coupling

We study the spatial coherence properties of a system composed of periodic silver nanoparticle arrays covered with fluorescent organic molecule film [1]. The evolution of spatial coherence of the structure is investigated both in weak and strong coupling regimes by systematically varying the coupling strength between the localized molecular excitons and the collective, delocalized modes of the nanoparticle array known as surface lattice resonances (SLRs). In stark contrast to pure localized excitons, the high degree of spatial coherence is maintained in the strong coupling regime, even when the mode is very exciton-like (80%). The results of our recent luminescence experiments will be presented. The effects of spin-orbit coupling are studied in periodic rectangular arrays of magnetic Ni nanoparticles [2]. We observe SLR modes in which the two directions of the lattice are coupled by the magnetic-field-controllable spin-orbit coupling in the nanoparticles. When breaking the symmetry of the lattice, we find that the optical response shows Fano-type surface lattice resonances whose frequency is determined by the periodicity orthogonal to the polarization of the incident field. In striking contrast, the magneto-optical Kerr response is controlled by the period in the parallel direction. The spectral separation of the response for longitudinal and orthogonal excitations provides versatile tuning of narrow and intense magneto-optical resonances.