The resonant x-ray scattering (magnetic elastic, RXMS, and inelastic, RIXS) of ${\mathrm{Ir}}^{4+}$ at the $L_{2,3}$ edges relevant to spin-orbit Mott insulators $A_{n+1}{\mathrm{Ir}}_n{\mathrm{O}}_{3n+1}$ ($A=\mathrm{Sr}$, Ba, etc.) are calculated using a single-ion model which treats the spin-orbit and tetragonal crystal-field terms on an equal footing. Both RXMS and RIXS in the spin-flip channel are found to display a nontrivial dependence on the direction of the magnetic moment, $\mathit{\mu }$. Crucially, we show that for $\mathit{\mu }$ in the $ab$ plane, RXMS in the cross-polarized channel at the $L_2$ edge is zero irrespective of the tetragonal crystal field; spin-flip RIXS, relevant to measurements of magnons, behaves reciprocally, being zero at $L_2$ when $\mathit{\mu }$ is perpendicular to the $ab$ plane. Our results have important implications for the assignment of a $j_{\mathrm{eff}}=1/2$ ground state on the basis of resonant x-ray experiments.

• Received 26 July 2013

DOI:https://doi.org/10.1103/PhysRevLett.112.026403