Spin and orbital dynamics through the metal-to-insulator transition in Cd\(_2\)Os\(_2\)O\(_7\) probed with high-resolution RIXS

Abstract

High-resolution resonant inelastic x-ray scattering measurements (\(\Delta E\) = 46 meV) have been performed on Cd\(_2\)Os\(_2\)O\(_7\) through the metal-to-insulator transition (MIT). A weakly dispersive magnetic excitation at 120 meV evolves continuously through the MIT, in agreement with recent Raman scattering results, and provides further confirmation for an all-in, all-out magnetic ground state. Asymmetry of this feature is likely a result of coupling between the electronic and magnetic degrees of freedom. We also find that the orbital excitations exhibit a degree of \(5d^4\) character, which differs from the nominal \(5d^3\). This has been verified by semiempirical ligand field theory and ab initio quantum chemistry calculations. We explore the possible origins for this behavior, including the possibility that the free ion model breaks down for Cd\(_2\)Os\(_2\)O\(_7\).