Magnetic excitations in a three-orbital model for the strongly spin-orbit coupled iridates: Effect of mixing between the J=1/2 and 3/2 sectors

A three-orbital-model approach for studying spin wave excitations in the strongly spin-orbit coupled layered perovskite iridates is presented which provides a unified description of magnetic excitations as well as the electronic band structure. The calculated spin wave dispersions with realistic three-band parameters are in excellent agreement with the RIXS data for iridates, including the strong AF zone boundary dispersion in the single-layer compound $\rm Sr_2 Ir O_4$ and the large anisotropy gap in the bilayer compound $\rm Sr_3 Ir_2 O_7$. The RIXS spin wave data is shown to provide evidence of mixing between the J=1/2 and 3/2 sectors in both compounds.