Spin-orbit excitons and electronic configuration of the 5d4 insulator Sr3Ir2O7F2

Here, we report on the low-energy excitations within the paramagnetic spin-orbit insulator Sr3Ir2O7F2 studied via resonant inelastic x-ray scattering, ab initio quantum chemical calculations, and model Hamiltonian simulations. This material is a unique d4 Ir5+ analog of Sr3Ir2O7 that forms when F ions are intercalated within the SrO layers spacing the square lattice IrO6 bilayers of Sr3Ir2O7. Due to the large distortions about the Ir5+ ions, our computations demonstrate that a large single-ion anisotropy yields an S = 1 (L approximate to 1, J approximate to 0) ground-state wave function. Weakly coupled, excitonic modes out of the Sz = 0 ground state are observed and are well described by a phenomenological spin-orbit exciton model previously developed for 3d and 4d transition metal ions. The implications of our results regarding the interpretation of previous studies of hole-doped iridates close to d4 fillings are discussed.