Magnetic excitation spectrum of Na 2 IrO 3 probed with resonant inelastic x-ray scattering

Abstract

The low energy excitations in Na 2 IrO 3 have been investigated using resonant inelastic x-ray scattering (RIXS). A magnetic excitation branch can be resolved, whose dispersion reaches a maximum energy of about 35 meV at the Γ point. The momentum dependence of the excitation energy is much larger along the Γ − X direction compared to that along the Γ − Y direction. The observed dispersion relation is consistent with a recent theoretical prediction based on the Heisenberg-Kitaev model. At high temperatures, we find large contributions from lattice vibrational modes to our RIXS spectra, suggesting that a strong electron-lattice coupling is present in Na 2 IrO 3 .