We investigated the temperature-dependent evolution of the electronic structure of the $J_{\text{eff}}=\frac{1}{2}$ Mott insulator ${\text{Sr}}_2{\text{IrO}}_4$ using optical spectroscopy. The optical conductivity spectra $\sigma \left(\omega \right)$ of this compound has recently been found to exhibit two $d\text{−}d$ transitions associated with the transition between the $J_{\text{eff}}=\frac{1}{2}$ and $J_{\text{eff}}=\frac{3}{2}$ bands due to the cooperation of the electron correlation and spin-orbit coupling. As the temperature increases, the two peaks show significant changes resulting in a decrease in the Mott gap. The experimental observations are compared with the results of first-principles calculation in consideration of increasing bandwidth. We discuss the effect of the temperature change in the electronic structure of ${\text{Sr}}_2{\text{IrO}}_4$ in terms of local lattice distortion, excitonic effect, electron-phonon coupling, and magnetic ordering.

• Received 14 May 2009

DOI:https://doi.org/10.1103/PhysRevB.80.195110