| Summary: | Sr _2 IrO _4 was predicted to be an unconventional superconductor upon carrier doping since it highly resembles the high-temperature cuprates. Here, to understand carrier doping effect on spin–orbit coupled Mott insulator Sr _2 IrO _4 , the electronic structure and local structure distortion for Sr _2 − _x La _x IrO _4 system have been investigated by x-ray absorption spectroscopy. By comparing the intensity of white-line features at the Ir L _2,3 absorption edges, we observe remarkably large branching ratios in La-doped compounds, greater than that of the parent material Sr _2 IrO _4 , suggesting a strong spin-orbit interaction for Sr _2 IrO _4 -based system. Moreover, extended x-ray absorption fine structure spectra demonstrate more regular IrO _6 octahedra, i.e. the weakened crystal electric field versus La-doping. By theoretical calculations, the synergistic effect of regular IrO _6 octahedra and electron doping is established, which accounts for the transition from a Mott insulator to a conductive state in Sr _2 − _x La _x IrO _4 -based system.
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