Hybridized Magnon–Phonon Excitations in the Olivine-Type Silicate Co2SiO4

Magnons and phonons are collective excitations in crystals that behave as independent quasiparticles when weakly coupled. Strong magnetoelastic coupling, however, can open gaps at band crossings and give rise to hybridized quasiparticles known as magnon-polarons. These excitations offer a direct window into spin–lattice interactions and are predicted to host topological features such as finite Chern numbers and Berry curvature, but their direct observation in crystalline materials remains scarce. In this talk, I will introduce the olivine-type silicate family M2SiO4 (M = Co, Fe, Mn) as a promising platform for exploring these effects, with a focus on Co2SiO4. Earlier neutron scattering studies hinted at avoided crossings but lacked sufficient information for quantitative analysis. We revisit this system using modern time-of-flight neutron scattering to map out its excitation spectra across the entire Brillouin zone. We observe a complex hierarchy of hybridized excitations involving magnons, phonons, and spin excitons. We further use polarized neutron scattering to delineate the character of these excitations. By combining symmetry analysis, an effective spin model, and density functional theory phonon calculations, we develop a comprehensive understanding of hybridized modes in Co2SiO4. These results lay the groundwork for a complete understanding of magnetoelastic interactions across the M2SiO4 family.