A critical point in Sr2-xIrO4 and less distorted IrO6 octahedra induced by deep Sr-vacancies

摘要

For the Sr(2-x)lrO(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 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 Ir L-2,L-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. (C) 2017 Elsevier Ltd. All rights reserved.