The Electric Field Morphology of Plasmonic Picocavities

Picocavities are plasmonic nanostructures featuring atomistic defects within subnanometer gaps. Such a unique morphology enables extreme light confinement at subnanometer scales and drives substantial field enhancements with applications from molecular sensing to plasmon-driven catalysis. However, the impact of atomistic defects on the plasmonic field morphology, which ultimately determines light-matter interactions at the nanoscale, remains largely unexplored due to the limitations of traditional theoretical models. Here, we employ the frequency-dependent fluctuating charges and dipoles (ωFQFμ) approach, an atomistic yet computationally efficient method previously validated against time-dependent density functional theory calculations, to reveal the plasmonic field morphology in gold picocavities composed of thousands of atoms. Our results uncover pronounced field inhomogeneities induced by the atomic-scale defects, which may trigger novel effects where electric field gradients are pivotal. Our findings establish the physical foundations for rationalizing experimental observations and guiding the design of next-generation nanophotonic devices with unprecedented control over atomic-scale field confinement.