Monte carlo study of an unconventional superconducting phase in iridium oxide J_eff=1/2 mott insulators induced by carrier doping

Based on a microscopic theoretical study, we show that novel superconductivity is induced by carrier doping in layered perovskite Ir oxides where a strong spin-orbit coupling causes an effective total angular momentum J_eff=1/2 Mott insulator. Using a variational Monte Carlo method, we find an unconventional superconducting state in the ground state phase diagram of a t_2g three-orbital Hubbard model on the square lattice. This superconducting state is characterized by a d_x2-y2-wave "pseudospin singlet" formed by the J_eff=1/2 Kramers doublet, which thus contains interorbital as well as both singlet and triplet components of t_2g electrons. The superconducting state is found stable only by electron doping, but not by hole doping, for the case of carrier doped Sr₂IrO₄. We also study an effective single-orbital Hubbard model to discuss the similarities to high-T_c cuprate superconductors and the multiorbital effects.