Evolution of the electronic structure of Ru-doped single-crystal iridates

We investigated Ru-doped single-crystal iridates, , at three different doping concentrations (, 0.07, and 0.10) using optical spectroscopy. The undoped pristine compound () is known as a novel Mott insulator. Remarkably, the optical conductivity spectra of all three samples exhibited insulating behavior, although we observed weak Drude components in the optical conductivity spectra down to the lowest temperature of 30 K. The charge-carrier densities of the Ru-doped iridates estimated from the Drude components are significantly smaller than the expected values estimated from the nominal Ru-doping concentrations. Herein, we provide the temperature- and doping-dependent electronic structure evolution of Ru-doped iridates. We expect that our results will be useful for understanding the intriguing Ru-doping-dependent properties of iridate .