Observation of strong spin-orbit couplings in plasmonic spin-twistronics topological lattices.

Twistronics is based on the control of the relative twist angle between the two layers of two-dimensional (2D) material in a moiré superlattice. Manipulating the twist angle enables controlling a variety of nontrivial properties, making twistronics a platform revolutionizing electronics and material sciences. Here, we introduce spin-twistronics, which brings the principles of twistronics to topological spin photonics. The moiré superlattice is realized by stacking two spin lattices on a single surface plasmonic polariton (SPP) platform. Each 2D SPP wave supports the construction of topological lattices formed by photonic spins with specific topology governed by rotational and translational symmetries and intense spin-orbit couplings. We theoretically and experimentally demonstrate that a twisted bilayer of photonic spin lattices can produce moiré spin superlattices at specific angles. Modulating these periodically by the total angular momentum shows the emergence of spin quasiparticle topologies, such as real skyrmion lattices and meron clusters, multiple fractal patterns and slow-light control, properties that cannot be achieved in conventional plasmonic systems. Spin-twistronics creates multiple degrees of freedom to tune nontrivial nanophotonic properties for advances in on-chip information devices, optical manipulation, and chiral light-matter interactions.