The lattice Kerker effect refers to a strong suppression of reflected light from periodic arrays of scatterers in narrow spectral windows at normal incidence. It can occur when interference of scattered light from different multipolar modes from each unit cell and diffractive coupling among unit cells occur simultaneously. Here we investigate manifestations of the lattice Kerker effect in 1D arrays of planar plasmonic oligomer trimers. Numerical results computed using a coupled electric dipole model for 1D non-Bravais trimer arrays, where the three constituent particles in each trimer unit cell are explicitly included, are rationalized using a coupled electric and magnetic dipole model on a 1D Bravais lattice. This model allows the differential scattered power angular distributions from the array to be decomposed into the product of the angular distribution produced by a single unit cell containing colocalized electric and magnetic dipoles and the squared modulus of a structure factor accounting for diffraction arising from the periodic array. In addition to providing an intuitive explanation for characteristic signatures of the lattice Kerker effect at normal incidence, this model also enables the facile evaluation of angular scattered power distributions for non-normal angles of incidence. The results of this work expand the concept of the lattice Kerker effect in terms of both unit cell design and excitation conditions and provide a simple analytic model for designing periodic structures with engineered properties for applications in nanophotonics concerned with highly directional radiation beaming and enhanced magnetic field strengths at optical frequencies.

Emergent from the discrete spatial periodicity of plasmonic arrays, surface lattice resonances (SLRs) are characterized as dispersive, high-quality polaritonic modes that can be selectively excited at specific points in their photonic band structure by plane-wave light of varying frequency, polarization, and angle of incidence. Room-temperature Bose–Einstein condensation of exciton polaritons, lasing, and nonlinear matter-wave physics have all found origins in SLR systems, but to date, little attention has been paid to their thermal behavior. Here, we combine analytical theory and numerical calculations to investigate the photothermal properties of SLRs in periodic 1D and 2D arrays of plasmonic nanoparticles coupled to each other and to the electromagnetic far-field via transverse radiation. Specifically, we demonstrate how to create steady-state SLR thermal gradients spanning from the nanoscale to hundreds of microns that are actively controllable using light in spite of heat diffusion. We also demonstrate the surprising ability to localize thermal gradients at the lattice edges in topologically non-trivial SLR dimer lattices, thereby establishing a class of extraordinary thermal responses that are unconventional in ordinary materials. This work exposes a new direction in thermoplasmonics that has only just now begun to be explored.

Trimer meta-atoms composed of three gold rods in an equilateral triangular geometry were fabricated, and their near-field plasmonic responses were characterized via electron energy loss (EEL), cathodoluminescence (CL), and stimulated electron energy loss/gain (sEEL/sEEG) spectroscopy. The trimer structure hybridizes into a low-energy mode with all three rods coupling in-phase, which produces a circulating current and thus a magnetic field. The next highest-energy mode consists of two rods coupling out-of-phase and produces a net electric dipole. We investigate the near fields of hybridized magnetic and electric modes via EEL and CL and correlate their spectral characteristics and intensity maps. Then, by changing the length of the trimer rods, we tune the magnetic and electric modes to our laser energy and characterize the excited state via sEEL/sEEG spectroscopy. Exploration of the tilt dependence, relative to the optical source, of the two modes reveals that the electric mode sEEG intensity increases more than the expected sin 2 (θ) dependence of the optical electric field coupling (see the Supporting Information for a detailed description). After correcting for the tail of the close-proximity electric mode, we demonstrate sEEG via coupling of the magnetic component of the optical field to the magnetic meta-atoms, which has the expected cos 2 (θ) tilt dependence. This realization opens the possibility to explore the nanoscale excited-state near-field imaging of other magnetic meta-atom structures.

In this work, we characterize the near-field response of individual gold nanotriangles over a broad, visible-to-infrared, spectral region (200−1500 meV) using high-resolution electron energy-loss spectroscopy (EELS) performed inside of a scanning transmission electron microscope (STEM). We begin by experimentally imaging the spatial and spectral extent of each nanotriangle's plasmonic Fabry-Peŕot modes and measuring the evolution of their resonance energies with increasing edge length; thereby providing detailed information on infrared plasmon dephasing times and dispersion relations. Numerical electromagnetic simulations of the electron probe are used to interpret these experimental results and to compare the near-field electromagnetic enhancement factors of gold nanotriangles and nanorods of equal resonant energy. Taken together, this combined experimental and theoretical study provides unique insights relevant to designing noble metal plasmonic nanoparticle systems for solar energy harvesting and sensing applications in the near-and midinfrared.