Observation of Moiré Plasmonic Skyrmion Clusters

Abstract: Skyrmions are topological defects belonging to nontrivial homotopy classes in particle theory. Their remarkably stable topology has recently been observed in electromagnetic waves. For the evanescent fields near a surface, this has been realized so far only for elementary optical skyrmions, with a fixed skyrmion number. Here we report, both in theory and experiment, the concept of moir\'e plasmonic skyrmion clusters, where multi-skyrmions are nested to form a large optical skyrmion cluster. By leveraging twistronics engineering of plasmonic nanostructures, we demonstrate both crystallized and quasi-crystallized optical skyrmion lattices, revealing an unprecedented degree of topological control. In a misaligned composite nanostructure, the rapid inverting of optical skyrmion number is achieved, which is explained by a lattice model. This topological change of moir\'eplasmonic skyrmion clusters can serve as a precise beacon of the relative alignment deviation between composite nanostructures.