Spintwistronics: Photonic bilayer topological lattices tuning extreme spin-orbit interactions

Twistronics, the manipulation of Moiré superlattices via the twisting of two layers of two-dimensional (2D) materials to control diverse and nontrivial properties, has recently revolutionized the condensed matter and materials physics. Here, we introduce the principles of twistronics to spin photonics, coining this emerging field spintwistronics. In spintwistronics, instead of 2D materials, the two layers consist of photonic topological spin lattices on a surface plasmonic polariton (SPP) platform. Each 2D SPP wave supports the construction of topological lattices formed by photonic spins with stable skyrmion topology governed by rotational symmetry. By introducing spintwistronics into plasmonics, we demonstrate theoretically and experimentally that two layers of photonic spin lattices can produce Moiré spin superlattices at specific magic angles. These superlattices, modulated periodically by the quantum number of total angular momentum, exhibit novel properties-including new quasiparticle topologies, multiple fractal patterns, extremely slow-light control, and more-that cannot be achieved in conventional plasmonic systems. As a result, they open up multiple degrees of freedom for practical applications in quantum information, optical data storage and chiral light-matter interactions.

💡 Research Summary

The authors introduce “spintwistronics,” a new paradigm that extends the concept of twistronics—originally developed for moiré superlattices in stacked two‑dimensional (2D) materials—to the realm of spin photonics. Instead of atomically thin crystals, the two layers consist of photonic topological spin lattices patterned on a surface plasmon polariton (SPP) platform. Each SPP mode (TM polarization) supports a set of electric‑field components that can be expressed via a Hertz potential. From this potential the spin angular momentum (SAM) density is derived as a Berry‑curvature‑like quantity, establishing a direct spin‑orbit coupling (SOC) for the photonic field.

The building blocks are sub‑lattices with N‑fold rotational symmetry (C₃, C₄, C₆). By arranging N plane‑wave components with azimuthal angles θₙ = 2πn/N, the authors generate skyrmion‑like or meron‑like spin textures whose topological charge (skyrmion number n_sk) is determined by the symmetry and the total angular momentum (TAM) quantum number ℓ. The TAM ℓ = ℓ_orb + ℓ_spin adds an extra degree of freedom: varying ℓ changes the periodicity of the resulting moiré spin superlattice, the distribution of skyrmion charge, and the orientation of individual merons.

When two identical sub‑lattices are superimposed with a twist angle 2ϑ, a moiré spin superlattice forms. The twist angle must satisfy strict Diophantine relations (Eqs. 4‑6) involving integer pairs (m₁,m₂). For C₄ symmetry the condition is 2ϑ = arctan