Temperature dependence of the electronic structure of the Jeff = 1 2 Mott insulator Sr₂ IrO₄ studied by optical spectroscopy

We investigated the temperature-dependent evolution of the electronic structure of the Jeff = 1 2 Mott insulator Sr2 IrO4 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 Jeff = 1 2 and Jeff = 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 Sr2 IrO4 in terms of local lattice distortion, excitonic effect, electron-phonon coupling, and magnetic ordering.