Activating Hidden Magnons With Anomalous Rotational Symmetry

Correlated materials with competing spin–orbit and crystal‐field interactions can host composite spin–orbital magnons that are highly susceptible to structural and electronic perturbations, enabling the control of magnetic dynamics beyond spin‐only physics. Using Raman spectroscopy on , we show that the partial substitution of Ru with Mn reconstructs the magnon spectrum and reveals one–magnon modes that are hidden in the undoped state. We demonstrate that the transition‐metal substitution activates otherwise symmetry‐forbidden magnon modes through mirror‐symmetry breaking of the underlying spin–orbital configuration. This effect can be theoretically explained by the local structural distortions induced in the octahedra near the dopant, which enable the observation of mixed‐parity one–magnon modes. These excitations display a distinctive polarization dependence, with a lowering from fourfold to twofold rotational symmetry arising from the mixed‐parity character of the coupled magnons and interference between resonant and nonresonant scattering channels. Our results show that spin–orbit–lattice entanglement provides a route to tailoring collective magnetic excitations and their polarization response in spin–orbit–coupled correlated systems.