Epitaxial compressive strain effect in La3Ni2O7-δ thin films

Epitaxial strain provides an effective route to tune the structural and electronic properties of correlated oxide thin films. Here, to investigate the influence of in-plane compressive strain effect on La 3 Ni 2 O 7-δ thin films, we synthesize a series of samples on three compressively strained substrates. We observe that the resistance exhibits a metal-to-insulator transition behavior as the strain level increases. This is attributed to the aggravated oxygen deficiency in large compressive strain cases. Our theoretical calculations confirm that the formation energy of oxygen vacancies gradually decreases with the increase of in-plane compressive strain strengths, suggesting more serious oxygen content deviation. Furthermore, we also reveal that the γ band, dominated by Ni 3dz 2 orbitals, exhibits a dependent relationship with the compressive strain, which is gradually moving away from the Fermi energy as the strain increases. These results establish a correlation between epitaxial strain, oxygen vacancy formation, and electronic transport in La 3 Ni 2 O 7-δ thin films. Our work provides important insights into the compressive strain, oxygen defect, and electronic structure interplay in bilayer nickelates, which is essential for understanding and tuning their emergent physical properties.