Hierarchical Hybridization in Plasmonic Honeycomb Lattices.

This paper reports hierarchical hybridization as a mode-mixing scheme to account for the unique optical properties of non-Bravais lattices of plasmonic nanoparticles (NPs). The formation of surface lattice resonances (SLRs) mediated by multi-order localized surface plasmons (LSPs) can result in asymmetric electric near-field distributions surrounding the NPs. This asymmetry is due to LSP hybridization at the individual NP level from LSPs of different orders and at the unit-cell level (NP dimer) from LSPs of the same order. Fabricated honeycomb lattices of silver NPs exhibit ultra-sharp SLRs at the  point that can facilitate nanolasing. Modeling of the stimulated emission process revealed that the multipolar component of the lattice plasmon mode was responsible for the feedback for lasing. By leveraging multipolar LSP responses from aluminum NPs lattices, we achieved two distinct  point band-edge modes from a honeycomb lattice having only a single lattice spacing. This work highlights how multipolar LSP coupling in plasmonic lattices with a non-Bravais symmetry have important implications for designing SLRs and their associated plasmonic near-field distributions. These relatively unexplored degrees of freedom can decrease both ohmic and radiative losses in nanoscale systems and enable SLRs to build unanticipated connections between photonics and nanochemistry.