Temperature dependence of the electronic structure of the J_eff=1/2 Mott insulator Sr₂IrO₄ studied by optical spectroscopy

We investigated the temperature-dependent evolution of the electronic structure of the J_eff=1/2 Mott insulator Sr₂IrO₄ using optical spectroscopy. The optical conductivity spectra σ(ω) of this compound has recently been found to exhibit two d-d transitions associated with the transition between the J_eff=1/2 and J_eff=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 Sr₂IrO₄ in terms of local lattice distortion, excitonic effect, electron-phonon coupling, and magnetic ordering.