Testing the validity of the strong spin-orbit-coupling limit for   octahedrally coordinated iridates in a model system Sr$_3$CuIrO$_6$
  The electronic structure of Sr$_3$CuIrO$_6$, a model system for the 5d Ir ion in an octahedral environment, is studied through a combination of resonant inelastic x-ray scattering (RIXS) and theoretical calculations. RIXS spectra at the Ir L$_3$-edge reveal an Ir $t_{2g}$ manifold that is split into three levels, in contrast to the expectations of the strong spin-orbit-coupling limit. Effective Hamiltonian and $ab inito$ quantum chemistry calculations find a strikingly large non-cubic crystal field splitting comparable to the spin-orbit coupling, which results in a strong mixing of the $j_{\mathsf{eff}}=1/2$ and $j_{\mathsf{eff}}=3/2$ states and modifies the isotropic wavefunctions on which many theoretical models are based. 
X. Liu, Vamshi M. Katukuri, L. Hozoi, Wei-Guo Yin, M. P. M. Dean, M.   H. Upton, Jungho Kim, D. Casa, A. Said, T. Gog, T. F....
cond-mat.str-el