High-energy electronic excitations in Sr$_2$IrO$_4$ observed by Raman scattering

The interplay between spin-orbit interaction, on-site coulomb correlation, crystal field splitting, and inter-site hopping leads to a novel insulating behavior in Sr$_2$IrO$_4$ as the realization of the $J_{eff} =1/2$ state. We report results of a large-shift Raman scattering investigation of electronic excitations in Sr$_2$IrO$_4$. We found two high-energy excitations at 690 meV and 680 meV with $A_{1g}$ and $B_{1g}$ symmetry respectively. The two peaks have different temperature and Rh-doping dependences. Symmetry analysis of the dd transitions that contribute to Raman signals will also be presented. The observed peaks are consistent with the scenario of excitons associated with inter-site dd transitions without pseudospin-flip.