Two-magnon excitations in altermagnetism probed by inelastic light scattering

Altermagnetism is a recently discovered class of magnetic order that combines key features of both ferromagnetism and antiferromagnetism. In altermagnets, electronic states with opposite spins exhibit energy splitting due to the breaking of time-reversal symmetry, while the system retains a vanishing net magnetization. From the perspective of spin dynamics, magnons with left- and right-handed chirality in altermagnets also become non-degenerate, leading to a characteristic splitting in the spin-wave spectrum. These unconventional band splittings in the single-particle spectrum have become a defining signature for identifying altermagnetic order. However, in inelastic light scattering experiments, such as Raman scattering and Resonant inelastic x-ray scattering (RIXS), another important type of signal in antiferromagnetic systems, the two-magnon excitation, is overlooked in altermagnets. In this work, we theoretically investigate the two-magnon excitations and the corresponding RIXS spectra in altermagnetic systems. We demonstrate that the two-magnon RIXS spectra of altermagnets exhibit distinct features compared to those of conventional antiferromagnets, arising from the chirality-dependent magnon splitting and magnon–magnon interactions. Our findings indicate that two-magnon RIXS may serve as a novel probe for experimental characterization of altermagnets.