Quality factor of plasmonic monopartite and bipartite surface lattice resonances

Surface lattice resonance (SLR) is the collective excitation of nanoparticle resonances arising from the hybridization between localized surface plasmons (LSPs) and propagating Rayleigh anomalies (RAs). When comparing with the corresponding LSPs, SLRs exhibit a much higher quality factor. In fact, as the quality factor depends on the constituting resonances and their hybridization, how one can parametrize it in an analytic form is an important issue. We have studied the SLRs arising from two-dimensional Au monopartite nanoparticle arrays by angle- and polarization-resolved reflectivity spectroscopy, temporal coupled mode theory (CMT), and finite-difference time-domain simulation. The scattering matrix of the SLRs is formulated, revealing the importance of the spectral detuning and the interaction strengths between the LSP and the RAs in governing the quality factor. We then extend the CMT approach to study bipartite arrays where a nanoparticle dimer is employed and find the coupling between two LSPs plays a major role in further boosting the quality factor. Specifically, the coupling takes part in controlling the detuning factor as well as determining whether the coupled bright or dark mode is hybridized with the RAs. The dark mode hybridization can strongly enhance the quality factor, which is otherwise not possible in the monopartite counterparts.

Automated summary

Surface lattice resonance (SLR) is a collective excitation of nanoparticle resonances resulting from the hybridization of localized surface plasmons (LSPs) and propagating Rayleigh anomalies (RAs). The quality factor of SLRs depends on the spectral detuning and the interaction strengths between LSPs and RAs. Studying bipartite arrays involving nanoparticle dimers shows that the coupling between bright and dark modes can significantly enhance the quality factor, which is not achievable in monopartite arrays.