Resonant X-ray Diffraction Study of the Strongly Spin-Orbit-Coupled Mott Insulator CaIrO3

We performed resonant x-ray diffraction experiments at the L absorption edges for the post-perovskite-type compound CaIrO3 with a (t(2g))(5) electronic configuration. By observing the magnetic signals, we could clearly see that the magnetic structure was a striped ordering with an antiferromagnetic moment along the c axis and that the wave function of a t(2g) hole is strongly spin-orbit entangled, the J(eff) = 1/2 state. The observed spin arrangement is consistent with theoretical work predicting a unique superexchange interaction in the J(eff) = 1/2 state and points to the universal importance of the spin-orbit coupling in Ir oxides, independent of the octahedral connectivity and lattice topology. We also propose that nonmagnetic resonant scattering is a powerful tool for unraveling an orbital state even in a metallic iridate.