Microscopic Study of a Spin-Orbit-Induced Mott Insulator in Ir Oxides

Motivated by recent experiments of a novel 5d Mott insulator in Sr(2)IrO(4), we have studied the two-dimensional three-orbital Hubbard model with a spin-orbit coupling lambda. 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 lambda. 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 lambda, 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 Sr(2)IrO(4).