Transverse Spin Vortices and Skyrmions in the Electric Near-Field of Plasmonic Nanogaps

Topological quasiparticles such as skyrmions have been observed in the spin angular momentum density of propagating surface waves such as surface plasmon polaritons, but their spatial resolution remains diffraction limited. Here, we demonstrate the creation of few-nanometer-scale transverse spin textures with nontrivial topology near nanogaps formed by localized, oscillating charges. By tuning the phase delay between neighboring charges, a localized momentum flow emerges, encircled by a transverse spin vortex. The vortex orientation is dictated by left-handed spin-momentum locking, intrinsically linked to the transport of electric field saddle-point singularities across the nanogap. Increasing the number of oscillating charges leads to complex nanoscale spin angular momentum textures, including toroidal vortices and skyrmions. These results show that localized surface plasmon resonances in metallic multimer nanostructures enable the generation of deep-subwavelength electric field spin textures. This approach opens new pathways for controlling the spin properties of light at the nanoscale, far beyond the diffraction limit.