Coexistence of magnon-induced optical vortex and Gaussian beam scattering assisted by rotational umklapp process
Phys. Rev. B 114, 194428 – Published 28 October, 2026
DOI: https://doi.org/10.1103/qhyt-7fyd
Abstract
The exploitation of crystal-lattice symmetries to engineer angular momentum transfer between structured light and magnons marks a novel frontier for optomagnonic research. In Brillouin light scattering, when focused light propagates parallel to an external magnetic field and interacts with ferromagnetic uniform magnons, only optical vortex scattering is expected to be permitted. Due to the combined effects of magneto-optical coupling and optical spin-orbit interaction, the transfer of magnon spin angular momentum to photon orbital angular momentum allows for this distinctive scattering phenomenon. Here, we experimentally demonstrate that, for a specific ferromagnetic crystal orientation, Gaussian beam scattering coexists with the optical vortex scattering, contrary to conventional expectations based on angular momentum conservation between magnons and photons. We show that the crystal lattice, via the rotational umklapp process, provides the missing angular momentum required for the Gaussian beam scattering. Furthermore, our theoretical model predicts a focus-dependent efficiency crossover between Gaussian beam and optical vortex scattering as the numerical aperture increases.
