Influence of spatial dispersion on surface plasmons, nanoparticles, and grating couplers

Abstract

Recent experiments have shown that spatial dispersion may have a conspicuous impact on the response of plasmonic structures. This suggests that in some cases, the Drude model should be replaced by more advanced descriptions that take spatial dispersion into account, such as the hydrodynamic model. Here, we show that nonlocality in the metallic response affects surface plasmons propagating at the interface between a metal and a dielectric with high permittivity. As a direct consequence, any nanoparticle with a radius larger than 20 nm can be expected to be sensitive to spatial dispersion, whatever its size. The same behavior is expected for a simple metallic grating allowing the excitation of surface plasmons, just as in Wood’s famous experiment. Finally, we carefully set up a procedure to measure the signature of spatial dispersion precisely, leading the way for future experiments. Importantly, our work suggests that for any plasmonic structure in a high-permittivity dielectric, nonlocality should be taken into account.