Spectral Evidence of Correlation-Controlled Metal-Insulator Transition in Nd_1-xSr_xNiO₃ Thin Films

Epitaxial growth serves as a critical platform for tailoring electronic interactions. Here, we synthesized high-quality Nd_1-xSr_xNiO₃ thin films on (La_0.3Sr_0.7)(Al_0.65Ta_0.35)O₃ (LSAT) (001) and SrTiO₃ (STO) (001) substrates and systematically investigated the effects of substrate strain and chemical doping on their low-energy electronic structures using angle-resolved photoemission spectroscopy (ARPES). Transport measurements reveal that Sr doping strongly suppresses the metal-insulator transition (MIT) temperature T_MIT on both substrates, with accelerated suppression in STO (001)-grown samples. Our ARPES results reveal that beyond a chemical potential shift, Sr doping significantly alters the effective mass, with a larger change observed in Nd_1-xSr_xNiO₃/STO (001) than in LSAT-based films. These findings indicate that Sr doping, combined with epitaxial strain, alters the correlation strength, thereby modifying the MIT. Our results unravel the intricate interplay among multiple degrees of freedom in Nd_1-xSr_xNiO₃ thin films, deepening the understanding of nickelate-based heterostructure design and engineering.