Determination of Hund's coupling in 5d oxides using resonant inelastic x-ray scattering

We report resonant inelastic x-ray scattering (RIXS) measurements on ordered double-perovskite samples containing Re5+ and Ir5+ with 5d2 and 5d4 electronic configurations, respectively. In particular, the observed RIXS spectra of Ba2YReO6 and Sr2MIrO6 (M = Y, Gd) show sharp intra-t2g transitions, which can be quantitatively understood using a minimal “atomic” Hamiltonian incorporating spin-orbit coupling λ and Hund's coupling JH. Our analysis yields λ=0.38(2)eV with JH=0.26(2)eV for Re5+ and λ=0.42(2)eV with JH=0.25(4)eV for Ir5+. Our results provide sharp estimates for Hund's coupling in 5d oxides and suggest that it should be treated on equal footing with spin-orbit interaction in multiorbital 5d transition-metal compounds.