Spin-orbit coupling in iridium-based 5dcompounds probed by x-ray absorption spectroscopy

We have performed x-ray absorption spectroscopy (XAS) measurements on a\nseries of Ir-based 5d transition metal compounds, including Ir, IrCl3, IrO2,\nNa2IrO3, Sr2IrO4, and Y2Ir2O7. By comparing the intensity of the "white-line"\nfeatures observed at the Ir L2 and L3 absorption edges, it is possible to\nextract valuable information about the strength of the spin-orbit coupling in\nthese systems. We observe remarkably large, non-statistical branching ratios in\nall Ir compounds studied, with little or no dependence on chemical composition,\ncrystal structure, or electronic state. This result confirms the presence of\nstrong spin-orbit coupling effects in novel iridates such as Sr2IrO4, Na2IrO3,\nand Y2Ir2O7, and suggests that even simple Ir-based compounds such as IrO2 and\nIrCl3 may warrant further study. In contrast, XAS measurements on Re-based 5d\ncompounds, such as Re, ReO2, ReO3, and Ba2FeReO6, reveal statistical branching\nratios and negligible spin-orbit coupling effects.\n