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

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 3z(2) - r(2) 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 3z(2) - r(2) band surprisingly becomes 3D due to the Ni-La hybridization, and the La-5d xy orbital also forms a 2D metallic band. Therefore, La(n+1)NinO(2n+2) is a dimensionality-controlled insulator-metal crossover system. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.