Oxygen states in La- and Rh-doped Sr2IrO4 probed by angle-resolved photoemission and O K-edge resonant inelastic x-ray scattering

Iridates are often viewed as an equivalent of cuprates with strong spin-orbit coupling. As such, they offer a new way to study the physics of Mott insulators. The hybridization with oxygen is, of course, essential in both compounds and may play a crucial role in the doping process. It could be quite different in the two families, iridates being $5d$ transition metals with different orbital geometries. But this difference has not been studied in detail so far. We present a combined angle-resolved photoemission spectrescopy and O $K$-edge resonant inelastic x-ray scattering study to document this aspect in ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$, pure and doped with 4% La and 15% Rh. We evidence different charge transfer excitations and distinguish those associated with apical or in-plane oxygens. We observe a specific evolution of one excitation upon Rh doping, which suggests a more itinerant nature of the holes related to the apical oxygen. This gives information on the way doping proceeds in iridates.