In ${\mathrm{CaIrO}}_3$, electronic correlation, spin-orbit coupling, and tetragonal crystal field splitting are predicted to be of comparable strength. However, the nature of its ground state is still an object of debate, with contradictory experimental and theoretical results. We probe the ground state of ${\mathrm{CaIrO}}_3$ and assess the effective tetragonal crystal field splitting and spin-orbit coupling at play in this system by means of resonant inelastic x-ray scattering. We conclude that insulating ${\mathrm{CaIrO}}_3$ is not a $j_{\text{eff}}=1/2$ iridate and discuss the consequences of our finding to the interpretation of previous experiments. In particular, we clarify how the Mott insulating state in iridates can be readily extended beyond the $j_{\text{eff}}=1/2$ ground state.

• Received 27 January 2014

DOI:https://doi.org/10.1103/PhysRevLett.112.176402