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 La₃Ni₂O₇. However, research on modulating the structural and transport characteristics of La₃Ni₂O₇ films by applying “chemical” compressive pressure through cation substitution is still limited. Here, we address this issue in the La_3−xNd_xNi₂O₇ (x = 0, 1.0, 1.5, 2.0, and 2.5) thin film samples. It was found that using Nd³⁺ with a smaller radius instead of La³⁺ 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_1.5Nd_1.5Ni₂O₇ sample was the smallest, which to some extent explains the changes in T_MIT. The Kondo effect dominates in other La_3−xNd_xNi₂O₇ (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.