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

Abstract

Sr${}_{3}$Ir${}_{2}$O${}_{7}$ exhibits a novel ${J}_{\mathrm{eff}}=\frac{1}{2}$ insulating state that features a splitting between ${J}_{\mathrm{eff}}=\frac{1}{2}$ and $\frac{3}{2}$ bands due to spin-orbit interaction. We report a metal-insulator transition in Sr${}_{3}$Ir${}_{2}$O${}_{7}$ via either dilute electron doping (La${}^{3+}$ for Sr${}^{2+}$) or application of high pressure up to 35 GPa. Our study of single-crystal Sr${}_{3}$Ir${}_{2}$O${}_{7}$ and (Sr${}_{1\ensuremath{-}x}$La${}_{x}$)${}_{3}$Ir${}_{2}$O${}_{7}$ 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 \ensuremath{\theta}. In contrast, slight doping of La${}^{3+}$ ions for Sr${}^{2+}$ ions in Sr${}_{3}$Ir${}_{2}$O${}_{7}$ readily induces a robust metallic state in the resistivity at low temperatures; the magnetic ordering temperature is significantly suppressed but remains finite for (Sr${}_{0.95}$La${}_{0.05}$)${}_{3}$Ir${}_{2}$O${}_{7}$ where the metallic state occurs. The results are discussed along with comparisons drawn with Sr${}_{2}$IrO${}_{4}$, a prototype of the ${J}_{\mathrm{eff}}=\frac{1}{2}$ insulator.