Mixing between J_eff=12 and 32 orbitals in Na²IrO ³: A spectroscopic and density functional calculation study

We investigated the electronic structure of Na²IrO³ using optical spectroscopy, first-principles calculation, and x-ray absorption spectroscopy. We found that the electronic structure of Na²IrO ³ is mainly determined by anisotropic hopping interactions and spin-orbit coupling. Due to the hopping interaction, the orbital character of the bands near the Fermi level deviates from the spin-orbit coupling-induced J_eff = 1/2 states. Polarization-dependent O 1s x-ray absorption spectroscopy showed that the J_eff = 1/2 state of an Ir atom can be mixed with the J_eff = 3/2 state of the neighboring Ir atom. This result implies that mixing between the J_eff = 1/2 and 3/2 states in the valence state should be carefully considered in proposed exotic states of Na²IrO³, such as topological insulator and quantum spin liquid states.