Orbital occupancies and the putative j(eff)=1/2 ground state in Ba2IrO4: 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, Delta approximate to 50(50) meV. We thus conclude definitively that Ba2IrO4 is a close realization of a spin-orbit Mott insulator with a j(eff) = 1 2 ground state, thereby overcoming ambiguities in this assignment associated with the interpretation of x-ray resonant scattering experiments.