Thickness-Dependent Metal-Insulator Transitions in SrIrO₃ Thin Films with SrTiO₃ Capping Layers

Iridate compounds, particularly Sr₂IrO₄ and SrIrO₃, have attracted significant interest due to their unique electronic and magnetic properties arising from strong spin-orbit coupling (SOC) and electron correlation effects. In previous experiments, we utilized pulsed laser deposition (PLD) to grow SrIrO₃ thin films on SrTiO₃ substrates, achieving either metal-like or insulator-like resistive behavior depending on the growth conditions. By examining the resistance as a function of film thickness, we observed that the metal-like SrIrO₃ films exhibit a metal-insulator transition (MIT) at 3 u.c., indicating that as the film thickness decreases, the band structure evolves similarly to that of Sr₂IrO₄, leading to increased resistivity. Conversely, insulator-like films exhibit an MIT at 7 u.c., which we attribute to Anderson localization driven by disorder. We subsequently deposited SrTiO₃ capping layers on each sample to investigate their effect on the resistance of SrIrO₃ films. In both cases, the MIT was suppressed, with the films exhibiting metal-like characteristics at reduced thicknesses. Notably, the SrTiO₃ capping layer induced a metal-like state even in the insulator-like films. XRD analysis revealed that the lattice constant of the insulator-like SrIrO₃ film shifted to match that of the metal-like SrIrO₃ upon SrTiO₃ capping. These results suggest that the SrTiO₃ capping layer reduces defects and disorder in the SrIrO₃ films, effectively mitigating Anderson localization and promoting metallic behavior.