Tuning the J_eff=12 insulating state via electron doping and pressure in the double-layered iridate Sr₃Ir₂O₇

Sr₃Ir₂O₇ exhibits a novel J _eff=12 insulating state that features a splitting between J _eff=12 and 32 bands due to spin-orbit interaction. We report a metal-insulator transition in Sr₃Ir₂O₇ via either dilute electron doping (La3⁺ for Sr2⁺) or application of high pressure up to 35 GPa. Our study of single-crystal Sr ₃Ir₂O₇ and (Sr_1-xLa _x)₃Ir₂O₇ reveals that application of high hydrostatic pressure P leads to a drastic reduction in the electrical resistivity by as much as six orders of magnitude at a critical pressure P _C = 13.2 GPa, manifesting a closing of the gap; but further increasing P up to 35 GPa produces no fully metallic state at low temperatures, possibly as a consequence of localization due to a narrow distribution of bonding angles θ. In contrast, slight doping of La3⁺ ions for Sr2⁺ ions in Sr₃Ir₂O₇ readily induces a robust metallic state in the resistivity at low temperatures; the magnetic ordering temperature is significantly suppressed but remains finite for (Sr_0.95La_0.05)₃Ir₂O₇ where the metallic state occurs. The results are discussed along with comparisons drawn with Sr₂IrO₄, a prototype of the J _eff=12 insulator.