Disorder suppression and tunable localization in ultrathin SrIrO₃ films via SrTiO₃ capping

Strong spin-orbit coupling in 5d transition-metal oxides produces correlated electronic phases that are highly sensitive to disorder and dimensionality. Here, we investigate the thickness-dependent transport of epitaxial SrIrO₃ (SIO) thin films, comparing insulator-like (SIO_i) and metal-like (SIO_m) types. Without capping, SIO_i localizes at 7 unit cells (u.c.), while SIO_m localizes at 3 u.c., revealing distinct disorder thresholds. Notably, applying a SrTiO₃ (STO) capping layer suppresses localization in both types. The critical thickness for the metal-insulator transition decreases to below 3 u.c. for SIO_i and to 2 u.c. for SIO_m. Structural analysis suggests that the STO capping mitigates intrinsic disorder by inducing lattice relaxation in the ultrathin films. This approach offers a pathway to control electronic phases in correlated oxide heterostructures via interface engineering.