Unveiling Hidden Magnons with Anomalous Rotational Symmetry
Abstract
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 Ca2RuO4, 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 RuO6 octahedra near the dopant, that 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.
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