Complex orbital state stabilized by strong spin-orbit coupling in a metallic iridium oxide IrO2

Resonant x-ray diffraction experiments were performed for the metallic iridium oxide IrO2. We observed anisotropic tensor of susceptibility (ATS) scattering, the spectrum of which shows a sharp contrast between the L-3 and L-2 edges. At the L-3 edge, resonance excitations were clearly observed from the core 2p orbitals to both the 5d t(2g) and e(g) orbitals. In contrast, the resonance mode associated with 5d t(2g) orbitals was indiscernible at the L-2 edge. This contrasting behavior indicates that Ir 5d t(2g) orbitals are fairly close to the J(eff) = 1/2 state due to the strong spin-orbit coupling in 5d transition-metal ions, as in the Mott insulator Sr2IrO4. Our results clearly demonstrate that ATS scattering is a useful probe for investigating complex orbital states in a metallic material, where novel phenomena such as the spin Hall effect are expected. DOI: 10.1103/PhysRevB.87.161111