Magnetic excitations in the square-lattice iridate Ba2IrO4

Abstract

We report a resonant inelastic x-ray scattering investigation of ultrathin epitaxial films of ${\mathrm{Ba}}_{2}{\mathrm{IrO}}_{4}$, and compare their low-energy magnetic and spin-orbit excitations to those of their sister compound ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$. Due to the ${180}^{\ensuremath{\circ}}$ Ir-O-Ir bond, the bandwidth of the magnon and spin orbiton is significantly larger in ${\mathrm{Ba}}_{2}{\mathrm{IrO}}_{4}$, making it difficult to describe these two types of excitations as separate well-defined quasiparticles. Both types of excitations are found to be quite sensitive to the effect of epitaxial strain. In addition, we find that the $d$-level inversion observed in ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ is absent in ${\mathrm{Ba}}_{2}{\mathrm{IrO}}_{4}$, as predicted in recent theoretical studies. Our results illustrate that the magnetic properties of ${\mathrm{Ba}}_{2}{\mathrm{IrO}}_{4}$ are substantially different from those of ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$, suggesting that these materials need to be examined more carefully with electron itinerancy taken into account.