Resonant inelastic x-ray scattering in double perovskites from first-principles. II. Ba2YB′O6 (B′ = Os and Ir)

We have investigated the electronic structure of the Ba ₂YB ′ O ₆ (B ′ = Os and Ir) double perovskites (DP) with the 5 d 3 and 5 d 4 configuration, respectively, within the density-functional theory (DFT) using the generalized gradient approximation while taking into account strong Coulomb correlations (GGA ＋ SO ＋ U ) in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. The GGA ＋ SO approximation produces a metallic ground state in Ba ₂YIrO ₆ and Ba ₂YOsO ₆, in contradiction with resistivity measurements and inelastic neutron data, which claim that both DPs are Mott insulators. To produce the correct ground state Hubbard electron–electron correlations must be taken into account. We have investigated resonant inelastic x-ray scattering (RIXS) spectra at the Os L 3 and Ir L 3 edges in Ba ₂YOsO ₆ and Ba ₂YIrO ₆, respectively. The calculated results are in good agreement with experimental data. The experimentally measured RIXS spectrum of Ba ₂YOsO ₆ at the Os L 3 edge in addition to the elastic scattering peak at 0 eV possesses a sharp feature below 3 eV corresponding to transitions within Os t 2 g levels. The excitation located from 3 to 6 eV is due to the t 2 g → e g interband transitions. The third wide structure situated at 5.5–9 eV appears due to ligand-to-metal charge transfer excitation: d − d transitions between Os 5 d O states derived from the tails of oxygen 2 p states and t 2 g states. A small high energy structure at 9–12 eV is due to 5 d O → e g transitions. In Ba ₂YIrO ₆, transitions within Ir t 2 g levels at the Ir L 3 edge give two very sharp peaks below 0.8 eV, t 2 g → e g transitions are located from 2.8 to 4.5 eV, the fine structure from 4.5 to 7.3 eV with a high-energy shoulder at around 6.3 eV is due to 5 d O → t 2 g transitions, and the high-energy structure which is extended from 7.5 up to 11 eV is due to 5 d O → e g transitions. We provide also the theoretical calculations of the optical conductivity spectra in these perovskites. The optical absorption peaks of Ba ₂YIrO ₆ and Ba ₂YOsO ₆, despite the similarity in shape, reveal a systematic difference in the peak widths and energy positions due to the differences in the band structures of the DPs.