Magnetic excitation spectrum of Na2IrO3 probed with resonant inelastic x-ray scattering

TL;DR

This study uses resonant inelastic x-ray scattering to investigate the magnetic excitations in Na2IrO3, revealing a dispersive magnetic mode, anisotropic dispersion, and significant electron-lattice interactions.

Contribution

First direct measurement of magnetic excitation dispersion in Na2IrO3 using RIXS, confirming theoretical Heisenberg-Kitaev model predictions and highlighting strong electron-lattice coupling.

Findings

Magnetic excitation branch reaches ~35 meV at b3-point.

Dispersion is highly anisotropic along b3-X and b3-Y directions.

Strong electron-lattice coupling evidenced by vibrational contributions at high temperatures.

Abstract

The low energy excitations in Na2IrO3 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 \Gamma-point. The momentum dependence of the excitation energy is much larger along the \Gamma-X direction compared to that along the \Gamma-Y direction. The observed dispersion relation is consistent with a recent theoretical prediction based on 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 Na2IrO3.