M-Point Lasing in Plasmonic Honeycomb Lattices

Honeycomb lattices can be defined as hexagonal lattices with a two-nanoparticle (NP) unit cell or considered as a superposition of two identical, but inequivalent hexagonal sublattices. Due to their non-Bravais nature, honeycomb NP lattices exhibit unique optical properties. For instance, honeycomb lattices have received attention for their ability to host topological edge states at the Γ and K points of photonic crystals. When the unit cell is redefined to consist of six NPs, edge states can be accessed at the Γ point of the lattice by deforming the unit cell while preserving its C_6v symmetry. If a honeycomb lattice is designed with a unit cell consisting of two NPs with inequivalent radii, the mirror and inversion symmetry of the lattice is broken, allowing edge states to emerge at the K points of photonic crystals. To assess the prospects of experimentally realizing topological states in plasmonic honeycomb NP lattices, a deeper understanding of their off-normal, high symmetry points is necessary. This presentation discusses the observation of band-edge states at the M point of Ag NP honeycomb lattices. Honeycomb lattices support the emergence of two surface lattice resonances (SLRs) at the M point: (1) a blue-shifted SLR_M1 due to coupling of two distinct out-of-plane dipole resonances; and (2) a red-shifted SLR_M2 resulting from in-plane dipole-dipole coupling. Although honeycomb lattices support two M-point SLR modes, only one mode supported lasing when organic dye solution was used as gain with the Ag NP lattices. This study demonstrates the unique coupling interactions at high symmetry points of non-Bravais plasmonic lattices.¹<br/>1. Juarez, X. G.; Li, R.; Guan, J.; Reese, T.; Schaller, R. D.; Odom, T. W., M-Point Lasing in Hexagonal and Honeycomb Plasmonic Lattices. <i>ACS Photonics </i><b>2022,</b> <i>9</i> (1), 52-58.