Orbital occupancies and the putative j eff = 1 2 ground state in Ba 2 IrO 4: A combined oxygen K -edge XAS and RIXS study

The nature of the electronic ground state of Ba2IrO4 has been addressed using soft x-ray absorption and inelastic scattering techniques in the vicinity of the oxygen K edge. From the polarization and angular dependence of x-ray absorption spectroscopy (XAS) we deduce an approximately equal superposition of xy, yz, and zx Ir4+ 5d orbitals. By combining the measured orbital occupancies, with the value of the spin-orbit coupling provided by resonant inelastic x-ray scattering (RIXS), we estimate the crystal field splitting associated with the tetragonal distortion of the IrO6 octahedra to be small, Δ≈50(50) meV. We thus conclude definitively that Ba2IrO4 is a close realization of a spin-orbit Mott insulator with a jeff=12 ground state, thereby overcoming ambiguities in this assignment associated with the interpretation of x-ray resonant scattering experiments.