Dimensionality-Driven Metal-Insulator Transition in Spin-Orbit-Coupled IrO2

A metal-insulator transition is observed in spin-orbit-coupled IrO2 thin films upon reduction of the film thickness. In the epitaxially grown samples, the critical thickness (t : 1.5-2.2 nm) is found to depend on the growth orientation (001), (100) or (110). Interestingly from the applied point of view, the insulating behavior is found even in polycrystalline ultrathin films. By analyzing the experimental electrical response with various theoretical models we find good fits to the Efros-Shklovskii-VRH and the Arrhenius-type behaviors, which suggests an important role of electron correlations in determining the electrical properties of IrO2. Our magnetic measurements also point to a significant role of magnetic order. All together, our results would point to a mixed Slaterand Mott-type of insulator.