We present a simple technique to calculate spin-orbit coupling, ⟨L⋅S⟩, and branching ratio measured in x-ray absorption spectroscopy. Our method is for first-principles electronic structure calculation and its implementation is straightforward for any of standard formulations and codes. We applied this technique to several different large spin-orbit coupling iridates. The calculated ⟨L⋅S⟩ and branching ratio of a prototype jeff=1/2 Mott insulator, Sr2IrO4, are in good agreement with recent experimental data over the wide range of Rh-doping. Three different double perovskite iridates (namely, Sr2MgIrO6, Sr2ScIrO6, and Sr2TiIrO6) are also well described. This technique can serve as a promising tool for studying large spin-orbit coupling materials from first-principles and for understanding experiments.
@article{arxiv.1608.06388,
title = {Calculating branching ratio and spin-orbit coupling from first-principles: A formalism and its application to iridates},
author = {Jae-Hoon Sim and Hongkee Yoon and Sang Hyeon Park and Myung Joon Han},
journal= {arXiv preprint arXiv:1608.06388},
year = {2016}
}