title: Microscopic study of a spin-orbit-induced Mott insulator in Ir oxides.
abstract: Motivated by recent experiments of a novel 5d Mott insulator in Sr2IrO4, we have studied the two-dimensional three-orbital Hubbard model with a spin-orbit coupling λ. The variational Monte Carlo method is used to obtain the ground state phase diagram with varying an on-site Coulomb interaction U as well as λ. It is found that the transition from a paramagnetic metal to an antiferromagnetic insulator occurs at a finite U=U(MI), which is greatly reduced by a large λ, characteristic of 5d electrons, and leads to the "spin-orbit-induced" Mott insulator. It is also found that the Hund's coupling induces the anisotropic spin exchange and stabilizes the in-plane antiferromagnetic order. We have further studied the one-particle excitations by using the variational cluster approximation and revealed the internal electronic structure of this novel Mott insulator. These findings are in agreement with experimental observations on Sr2IrO4.
authors.affiliation: Computational Condensed Matter Physics Laboratory, RIKEN ASI, Wako, Saitama 351-0198, Japan. h-watanabe@riken.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Watanabe
authors.forename: Tomonori
authors.initials: T
authors.lastname: Shirakawa
authors.forename: Seiji
authors.initials: S
authors.lastname: Yunoki