Dispersive magnetic and electronic excitations in iridate perovskites probed by oxygen <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>K</mml:mi></mml:math>-edge resonant inelastic x-ray scattering

Abstract

Resonant inelastic x-ray scattering (RIXS) experiments performed at the oxygen $K$ edge on the iridate perovskites ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ and ${\mathrm{Sr}}_{3}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ reveal a sequence of well-defined dispersive modes over the energy range up to $\ensuremath{\sim}0.8\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. The momentum dependence of these modes and their variation with the experimental geometry allows us to assign each of them to specific collective magnetic and/or electronic excitation processes, including single and bimagnons, and spin-orbit and electron-hole excitons. We thus demonstrate that dispersive magnetic and electronic excitations are observable at the O $K$ edge in the presence of the strong spin-orbit coupling in the $5d$ shell of iridium and strong hybridization between Ir $5d$ and O $2p$ orbitals, which confirm and expand theoretical expectations. More generally, our results establish the utility of O $K$-edge RIXS for studying the collective excitations in a range of $5d$ materials that are attracting increasing attention due to their novel magnetic and electronic properties. Especially, the strong RIXS response at O $K$ edge opens up the opportunity for investigating collective excitations in thin films and heterostructures fabricated from these materials.