Dimensionality-induced insulator-metal crossover in layered nickelates Lan+1NinO2n+2 (n = 2, 3, and ∞)

Abstract

Low-valence layered nickelates are a structural analog to the superconducting cuprates and possess interesting properties. In this work, we have systematically studied the electronic structure of Lan+1NinO2n+2 using first-principles calculations. Our results reveal that the Ni-3d 3z2 − r2 orbital state is active and evolves from discrete molecular levels to a continuous solid band and its filling varies as the dimensionality (or n) increases. The two-dimensional (2D) La3Ni2O6 and La4Ni3O8 are thus found to have a molecular insulating state. In contrast, the 3D LaNiO2 is metallic and its 3z2 − r2 band surprisingly becomes 3D due to the Ni-La hybridization, and the La-5d xy orbital also forms a 2D metallic band. Therefore, Lan+1NinO2n+2 is a dimensionality-controlled insulator-metal crossover system.