Resonant inelastic x-ray scattering investigation of Hund's and spin-orbit coupling in 5d2 double perovskites

B site ordered 5d2 double perovskites (A2BB′O6,B′=5d2) display a remarkable range of physical properties upon variation of the chosen B and B′ site ions. This sensitivity to chemical substitution reflects the delicate balance and profound impact of strong electronic correlation and spin-orbit coupling in such systems. We present rhenium L2 and L3 resonant inelastic x-ray scattering (RIXS) measurements of two such physically dissimilar materials, Mott-insultating Ba2YReO6 and semiconducting Sr2CrReO6. Despite these differences, our RIXS results reveal similar energy scales of Hund's (JH) and spin-orbit coupling (ζ) in the two materials, with both systems firmly in the intermediate Hund's coupling regime where JH/ζ∼1. However, there are clear differences in their RIXS spectra. The conductive character of Sr2CrReO6 broadens and obfuscates the atomic transitions within an electron-hole continuum, while the insulating character of Ba2YReO6 results in sharp atomic excitations. This contrast in their RIXS spectra despite their similar energy scales reflects a difference in the itinerancy-promoting hopping integral and illustrates the impact of the local crystal environment in double perovskites. Finally, L2 and L3 edge analyses of the atomic excitations in Ba2YReO6 reveal that the ordering of the low lying excited states is inverted compared to previous reports, such that the appropriate energy scales of Hund's and spin-orbit coupling are significantly modified. We present exact diagonalization calculations of the RIXS spectra at both edges which show good agreement with our results for new energy scales of ζ=0.290(5)eV and JH=0.38(2)eV [JH/ζ=1.30(5)].