A critical point in Sr2-IrO4 and less distorted IrO6 octahedra induced by deep Sr-vacancies

Abstract

For the Sr 2-x IrO 4 system, recent work pointed out the abnormal electronic and magnetic properties around a critical point. Here, to understand Sr-vacancy effect on spin-orbit coupled Mott insulator Sr 2 IrO 4 , the electronic structure and local structure distortion for Sr 2-x IrO 4 system have been investigated by x-ray absorption spectroscopy (XAS). By comparing the intensity of white-line features at the Ir L 2,3 -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 the Ir L 3 -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 IrO 6 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.