Spin-Disorder-Induced Raman Scattering in Europium Chalcogenides

The four independent symmetry components of first-order phonon Raman scattering in the paramagnetic phase of europium chalcogenides have been measured around the fundamental gap. The usually unobservable antisymmetric Γ₁₅⁺ component is found to be the largest one. The resonance enhancements of the different components, their relative intensities, and the scattered spectra are explained by a parameter-free microscopic theory which takes into account the spin disorder of the Eu²⁺ ions and the spin-orbit interaction of the $4f$ electrons.