Temperature-dependent electronic structure evolution of spin-orbit coupling induced Mott insulator Sr$_{2}$IrO$_{4}$

Recently, the effect of spin-orbit coupling in 5$d$ transition metal oxides attracted lots of attention. It was found that the cooperative interaction of spin-orbit coupling and electron correlation could realize unique Mott insulating ground state of Sr$_{2}$IrO$_{4}$. We investigated temperature-dependent optical conductivity spectra of 5$d$ Mott insulator Sr$_{2}$IrO$_{4}$. We observed drastic changes of the optical conductivity spectra. As temperature increases, the Mott gap was significantly reduced and spectral weight redistribution between the Ir $t_{2g}$ bands occurred. The electronic structure changes accompanied the change of optical phonon modes. These experimental observations could be understood in terms of the effects of spin-orbit and electron-lattice coupling.