Tuning of the Metal–Insulator Transition in Nd-Doped Bilayer Nickelate La₃Ni₂O₇ Thin Films

Abstract Recent studies have successfully demonstrated high- T c superconductivity in bilayer nickelate La 3 Ni 2 O 7 . However, research on modulating the structural and transport characteristics of La 3 Ni 2 O 7 films by applying “chemical” compressive pressure through cation substitution is still limited. Here, we address this issue in the La 3− x Nd x Ni 2 O 7 ( x = 0, 1.0, 1.5, 2.0, and 2.5) thin film samples. It was found that using Nd 3+ with a smaller radius instead of La 3+ can reduce the c -axis lattice constant and shift the metal–insulator transition (MIT) temperature T MIT . To probe the origin of the MIT at cryogenic temperatures, experimental measurements of magnetoresistance were conducted, and theoretical analysis was carried out using the Kondo model, Hikami–Larkin–Nagaoka equation, and other methods. The results indicate that as Nd doping rises, the contributions of the Kondo effect and two-dimensional weak localization (WL) first decrease and then increase. The total contribution of WL and the Kondo effect in the mid-doped La 1.5 Nd 1.5 Ni 2 O 7 sample was the smallest, which to some extent explains the changes in T MIT . The Kondo effect dominates in other La 3− x Nd x Ni 2 O 7 ( x = 0, 1.0, 2.0, and 2.5) samples. This work demonstrates that cation doping has a significant impact on bilayer nickelates, providing experimental evidence for understanding the physical mechanism of the MIT in bilayer nickelates.