Theoretical study of J_eff = 1/2 Mott insulator in Ir oxides: A strong spin-orbit coupling vs local electron correlations

The variational cluster approximation (VCA) is used to study the nature of a novel Mott insulator induced by a strong spin-orbit coupling along with moderate electron interactions for a two-dimensional three-band Hubbard model, consisting of the t₂g manifold of 5d orbitals, with five electrons (i.e., one hole) per site. To extend the variational space, we introduce a generalized local Kramer's doublet as a variational state for VCA We find that the Hund's coupling induces magnetic anisotropy and stabilizes in-plane antiferromagnetic order constructed by the Kramer's doublet. By carefully analyzing the expectation values of the generalized Kramer's double operator, we also find that the local hole state in the Mott insulator is comparable to the Kramer's doublet with J_eff = |S - L| =1/2.