Electronic structure of 5d transition-metal compounds

In this contribution, we describe fundamental electronic structures and spin-charge-orbital orderings of 5d transition-metal compounds. By reviewing photoemission spectroscopy studies on CuIr₂S₄, IrTe₂, Cs₂Au₂Br₆, and AuTe₂, we discuss the difference between the t _2g and e _g systems with respect to the spin-orbit splitting versus the Jahn-Teller splitting. In contrast to the Ir oxides with Mott-Hubbard character, the smallness of the charge-transfer energy plays essential roles in the exotic spin-charge-orbital orderings of the Ir and Au chalcogenides and halides. In particular, the Te 5p hole provides an interesting interplay between the charge-orbital order and the spin-orbit interaction in IrTe₂.