Enhanced insulating behavior in the Ir-vacant Sr2Ir1-xO4 system dominated by the local structure distortion.

Sr2IrO4, known as the Jeff = 1/2 Mott insulator, was predicted to be an unconventional superconductor upon doping since it highly resembles the high-temperature cuprates. However, recent work pointed out an enhanced insulating behavior in the Ir-vacant Sr2Ir1-xO4 system. In this contribution, to investigate the microscopic mechanism of its enhanced insulating behavior, X-ray absorption spectroscopy was applied to study the electronic structure and local structure distortion of Sr2Ir1-xO4. Due to the presence of Ir5+ ions, the preconceived holes are barely doped in the Ir-vacant system. Nevertheless, Ir vacancies finely modulate the local atomic structure, i.e. the topology of IrO6 octahedra and the in-plane Ir-O1-Ir bond angle. Combined with theoretical calculations, it is demonstrated that both the more distorted IrO6 octahedra and decreased Ir-O1-Ir angle contribute to the increment of the band gap, and then result in the enhanced insulating state for Sr2Ir1-xO4.