- Open Access
Symmetries of anisotropic spin interaction models
Phys. Rev. Research 8, 033327 – Published 16 September, 2026
DOI: https://doi.org/10.1103/ywpn-pt91
Abstract
We show that anisotropic spin interactions do not merely break spin-space group (SSG) symmetries, but instead twist them through cohomology invariants, yielding symmetry classes beyond subgroups of . This requires redefining the spin-only group in terms of proper spin rotations. Based on this unitary , we formulate a twisted SSG (tSSG) theory that captures the complete set of spin-space symmetries. We then study a spin-1 model with tSSG symmetry using linear flavor wave theory and find topological quadrupolar excitations defined on a spin Brillouin Klein bottle. Specifically, the quadrupolar excitations possess a momentum-space glide-reflection symmetry and the edge states exhibit a nonlocal momentum twist. These results establish the symmetry language required for interacting spin systems, whether realized in magnetic materials or on programmable quantum simulators, and open a route to unconventional magnetism.
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