Metal-insulator transition in layered nickelates La${}_{3}$Ni${}_{2}$O${}_{7\ensuremath{-}\ensuremath{\delta}}$ ($\ensuremath{\delta}$ $=$ 0.0, 0.5, 1)

Metal-insulator transition in layered nickelates La $_{3}$ Ni $_{2}$ O $_{7 - δ}$ ( $δ$ $=$ 0.0, 0.5, 1)

Victor Pardo and Warren E. Pickett

Phys. Rev. B 83, 245128 – Published 27 June 2011

Abstract

Three low-valence layered nickelates with general formula La $_{3}$ Ni $_{2}$ O $_{7 - δ}$ ( $δ$ $=$ 0.0, 0.5, 1) are studied by ab initio techniques. Both the insulating and the metallic limits are analyzed, together with the compound at the Mott transition ( $δ$ $=$ 0.5; Ni $^{2 +}$ ), that shows insulating behavior, with all Ni atoms in a $S$ $=$ 1 high-spin state. The compound in the $δ$ $=$ 1 limit (La $_{3}$ Ni $_{2}$ O $_{6}$ ), with mean formal valence Ni $^{1.5 +}$ and hence nominally metallic, nevertheless shows a correlated molecular insulating state, produced by the quantum confinement of the NiO $_{2}$ bilayers and the presence of mainly $d$ $_{z^{2}}$ bands (bonding-antibonding split) around the gap. The metallic compound shows a larger bandwidth of the $e_{g}$ states that can sustain the experimentally observed paramagnetic metallic properties. The evolution of the in-plane antiferromagnetic coupling with the oxygen content is discussed, and also the similarities of this series of compounds with the layered superconducting cuprates.