Charge ordering in Ir dimers in the ground state of Ba5AlIr2O11

It has been well established experimentally that the interplay of electronic correlations and spin-orbit interactions in Formula Presented and Formula Presented oxides results in insulating Formula Presented and Formula Presented ground states, respectively. However, in compounds where the structural dimerization of iridium ions is favorable, the direct Ir Formula Presented hybridization can be significant and takes a key role. Here, we investigate the effects of direct Ir Formula Presented hybridization in comparison with electronic correlations and spin-orbit coupling in Formula Presented, a compound with Ir dimers. Using a combination of ab initio many-body wave-function quantum chemistry calculations and resonant inelastic x-ray scattering experiments, we elucidate the electronic structure of Formula Presented. We find excellent agreement between the calculated and the measured spin-orbit excitations. Contrary to expectations, the analysis of the many-body wave function shows that the two Ir (Formula Presented and Formula Presented) ions in the Formula Presented dimer unit in this compound preserve their local Formula Presented character close to 1/2 and 0, respectively. The local point group symmetry at each of the Ir ions plays an important role, significantly limiting the direct Formula Presented hybridization. Our results emphasize that minute details in the local crystal field environment can lead to dramatic differences in the electronic states in iridates and Formula Presented oxides in general.