Magnetic excitation spectrum of Na<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>2</mml:mn></mml:msub></mml:math>IrO<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>3</mml:mn></mml:msub></mml:math>probed with resonant inelastic x-ray scattering

H. Gretarsson, J. P. Clancy, Yogesh Singh, P. Gegenwart, J. P. Hill, Jungho Kim, M. H. Upton, A. H. Said, D. Casa, T. Gög

Abstract

The low energy excitations in ${\mathrm{Na}}_{2}{\mathrm{IrO}}_{3}$ 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 $\ensuremath{\Gamma}$ point. The momentum dependence of the excitation energy is much larger along the $\ensuremath{\Gamma}\ensuremath{-}X$ direction compared to that along the $\ensuremath{\Gamma}\ensuremath{-}Y$ 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 ${\mathrm{Na}}_{2}{\mathrm{IrO}}_{3}$.

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