Dynamic Jahn-Teller effect and resonant inelastic x-ray scattering in cubic 5d² osmates.

Cubic 5d² double perovskites such as osmates attract growing attention due to their hidden orders. The osmates are cubic down to low temperature, and the ground states in the 5d² site are doubly degenerate. The intersite interactions between the doublet states give rise to either dipole-octupole or quadrupole orders. To fully understand the nature of the systems, concomitant treatment of all the interactions in the compounds will be decisive. The 5d² doublet can interact with lattice vibrations, resulting in the dynamic Jahn-Teller (JT) effect, whereas precise knowledge on the latter is missing. In this work, we theoretically evaluate the vibronic states of the dynamic JT center and predict the fingerprints of the dynamic JT effect in the Os L₃-edge and O K-edge resonant inelastic x-ray scattering (RIXS) spectra. The dynamic Jahn-Teller effect stabilizes the doubly degenerate states. The simulated RIXS spectra can show fine structures originating from the dynamic JT effect.