Thickness-Driven Metal-Insulator Transition in La₃Ni₂O₇ Thin Film

Recent studies have shown that bulk La₃Ni₂O₇ (LNO) exhibits superconductivity under high pressure below 80 K, while epitaxial LNO thin films only exhibit an insulating phase. Here, we report a film thickness-driven metal-insulator transition in encapsulated LNO thin films at room temperature. We deposit 2-48 nm epitaxial LNO thin film on the LaAlO₃ substrates using RF magnetron sputtering systems. These samples exhibit smooth surfaces with a typical surface roughness of about 5 Å. The room temperature resistivity shows a sharp decrease below 15 nm film thickness. In the thick films, the temperature dependence measurement of resistance shows an insulating behavior from 2 K to 300 K. In contrast, the 4.2 nm and 3.2 nm samples show metallic behavior at high temperatures, followed by a moderate resistance upturn at low temperatures. The resistance upturn temperature for the 3.2 nm sample is about 80 K. We discuss the effects of the capping layer and magnetic fields on the transport properties of the LNO thin films.