A topological lattice of plasmonic merons*

Topology is an emerging topic in physics, which explores geometrical properties that are impervious to continuous change in shape and size. Topological defects impart captivating emergent phenomena and serve as a bridge between microscopic, atomic, and even subatomic scales. Employing electromagnetic simulations and ultrafast, time-resolved photoemission electron microscopy, we describe the geometric transformation of normally incident circularly polarized optical fields from a square coupling structure, into surface plasmon polariton fields where the optical spin is converted into arrays of plasmonic vortices with orbital angular momentum. By electromagnetic simulation, we analyze how the spin orbit interaction molds the plasmonic orbital to spin angular momentum textures within each vortex domain into a lattice of plasmonic meron spin textures. We experimentally examine dynamics of the meron lattice by recording the ultrafast nanofemto plasmonic field evolution with deep subwavelength resolution and sub-optical cycle time accuracy. From these three-dimensional data we extract the linear polarization L-line singularity distribution with sub-diffraction limited resolution, and thereby define the meron periodic boundaries.