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

Recent studies have successfully demonstrated high-T_\rm c superconductivity in bilayer nickelate La_3Ni_2O_7. However, research on modulating the structural and transport characteristics of La_3Ni_2O_7 films by applying ``chemical" compressive pressure through cation substitution is still limited. Here, we address this issue in the La_3-xNd_xNi_2O_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_\rm 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_1.5Ni_2O_7 sample was the smallest, which to some extent explains the changes in T_\rm MIT. The Kondo effect dominates in other La_3-xNd_xNi_2O_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.