Optical study on the possible Slater insulator SrIr0.8Sn0.2O3

The orthorhombic perovskite iridate SrIr0.8Sn0.2O3 is reported to be a new candidate of Slater insulator at low temperatures. Here, we present optical spectroscopy measurements on SrIr0.8Sn0.2O3 at different temperatures (T) across the paramagnetic-antiferromagnetic phase transition. The low energy reflectivity decreases with reducing T . Six phonon peaks in the spectrum at low T are visible at room temperature, indicating the absence of crystal structure phase transition from 300 K to 10 K. The real part of conductivity spectra sigma(1)(omega) are obtained by employing the standard Kramers-Kronig transformation. In the paramagnetic state at room temperature, sigma(1)(omega) reaches a limiting value as omega -> 0, implying an electrical conducting state. Upon decreasing T, the low frequency sigma(1)(omega) decreases and approaches zero with a concomitant opening of a direct gap. Detailed analysis of the low energy data shows that the gap opening is continuous and sigma(1)(omega) at the low energy gap edge follows an unusual omega(1/2). dependence at low temperatures which is remarkably similar to other Slater insulators, such as NaOsO3.