We have investigated the excitation spectra of jeff=21 Mott insulator Na2IrO3. Taking into account a relativistic multiplet structure of Ir ions, we have calculated the optical conductivity σ(ω) and resonant inelastic x-ray scattering (RIXS) spectra, which manifest different features from those of a canonical jeff=21 system Sr2IrO4.Distinctly from the two-peak structure in Sr2IrO4, σ(ω) in Na2IrO3 has a broad single peak dominated by interband transitions from jeff=23 to 21. RIXS spectra exhibit the spin-orbit (SO) exciton that has a two-peak structure arising from the crystal-field effect, and the magnon peak at energies much lower than in Sr2IrO4. In addition, a small peak near the optical absorption edge is found in RIXS spectra, originating from the coupling between the electron-hole (e-h) excitation and the SO exciton. Our findings corroborate the validity of the relativistic electronic structure and importance of both itinerant and local features in Na2IrO3.
@article{arxiv.1307.0614,
title = {Electronic excitations in the edge-shared relativistic Mott insulator: Na$_2$IrO$_3$},
author = {Beom Hyun Kim and G. Khaliullin and B. I. Min},
journal= {arXiv preprint arXiv:1307.0614},
year = {2014}
}