Insulating nature of Na2 IrO3: Mott-type or Slater-type

We have investigated temperature-dependent electronic structures of Na2IrO3 to unravel its insulating nature. Employing the combined scheme of the density functional theory (DFT) and the dynamical mean-field theory (DMFT), we have shown that the insulating state persists even above the Néel temperature (TN), which reveals that Na2IrO3 is classified as a Mott-type insulator. The measured photoemission spectrum in the paramagnetic state is well described by the electronic structure obtained by the DFT+DMFT for the insulating state above TN. The analysis of optical conductivity, however, suggests that the nonlocal correlation effect is also important in Na2IrO3. Therefore, Na2IrO3 is not a standard Mott insulator in that the extended nature and the nonlocal correlation effect of Ir 5d electrons are important as well in describing its electronic and magnetic properties.