Resonant X-Ray Scattering and the j_eff=1/2 Electronic Ground State in Iridate Perovskites

The resonant x-ray scattering (magnetic elastic, RXMS, and inelastic, RIXS) of Ir4+ at the L-2,L-3 edges relevant to spin-orbit Mott insulators A(n+1) Ir(n)O3(n+1) (A = 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, mu. Crucially, we show that for 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 mu is perpendicular to the ab plane. Our results have important implications for the assignment of a j(eff) = 1/2 ground state on the basis of resonant x-ray experiments.