Sr-Doping-Modulated Metal-Insulator Transition in NdNiO₃ Epitaxial Films

Abstract Perovskite-structured nickelates, ReNiO 3 (Re = rare earth), have long garnered significant research interest due to their sharp and highly tunable metal-insulator transitions (MITs). Doping the parent compound ReNiO 3 with alkaline earth metal can substantially suppress this MIT. Recently, intriguing superconductivity has been discovered in doped infinite-layer nickelates (ReNiO 2 ), while the mechanism behind A-site doping-suppressed MIT in the parent compound ReNiO 3 remains unclear. To address this problem, we grew a series of Nd 1− x Sr x NiO 3 (NSNO, x = 0–0.2) thin films and conducted systematic electrical transport measurements. Our resistivity and Hall measurements suggest that Sr-induced excessive holes are not the primary reason for MIT suppression. Instead, first-principles calculations indicate that Sr cations, with larger ionic radius, suppress breathing mode distortions and promote charge transfer between oxygen and Ni cations. This process weakens Ni–O bond disproportionation and Ni 2+ /Ni 4+ charge disproportionation. Such significant modulations in lattice and electronic structures convert the ground state from a charge-disproportionated antiferromagnetic insulator to a paramagnetic metal, thereby suppressing the MIT. This scenario is further supported by the weakened MIT observed in the tensile-strained NSNO/SrTiO 3 (001) films. Our work reveals the A-side doping-modulated electrical transport of perovskite nickelate films, providing deeper insights into novel electric phases in these strongly correlated nickelate systems.