A critical point in Sr2-xIrO4 and less distorted IrO6 octahedra induced   by deep Sr-vacancies
  For the Sr2-xIrO4 system, recent work pointed out the abnormal electronic and magnetic properties around the critical point. Here, to understand Sr-vacancy effect on spin-orbit coupled Mott insulator Sr2IrO4, the electronic structure and local structure distortion for Sr2-xIrO4 system have been investigated by x-ray absorption spectroscopy (XAS). By comparing the intensity of white-line features at the IrL2,3-edge x-ray absorption near-edge spectroscopy (XANES), we observe a sudden rise of the branching ratio in the vicinity of the critical point.Further analysis on theIrL3 -edge extended x-ray absorption fine structure (EXAFS) and calculated data demonstrated that the abrupt enhancement of the branching ratio is intimately related to the less distorted IrO6 octahedra induced by deep Sr-vacancies, which in turn alters the relatively strength of the spin-orbit coupling (SOC) and crystal electric field (CEF)that would dictate the abnormal behavior of electronic and magnetic structure near the critical point. 
Jie Cheng, Shengli Liu, Bin Li, Haiyun Wang, Yu Wang and Wei Xu
cond-mat.str-el