Insulator-metal transition driven by change of doping and spin-orbit interaction in Sr2IrO4

Abstract

We have investigated the insulator-metal transition (IMT) of the 5d system Sr2IrO4 by optical spectroscopy. Change of the band filling as well as tuning of the spin-orbit interaction (SOI) strength has been realized in single crystalline thin films with continuous cation substitutions. Upon the IMT, the spectral weight of the Mott-gap region is transferred into the in-gap states, and its transfer rate was found to be enhanced similarly to those for the correlated electron system close to the IMT boundary. In particular, the SOI-controlled IMT leads to a characteristic spectral evolution as observed for bandwidth-controlled IMT. The observed feature unambiguously demonstrates the cooperative role of SOI and electron-correlation in realizing the Mott insulator state of Sr2IrO4.