Metal-insulator transition in a two-band model for the perovskite nickelates

TL;DR

This study models the metal-insulator transition in perovskite nickelates using a two-band approach, revealing the roles of Fermi surface nesting, Hund's coupling, and quantum confinement in their electronic and magnetic properties.

Contribution

Introduces a minimal two-band model for RNiO3 nickelates, analyzing charge, spin order, and quantum confinement effects across different interaction regimes.

Findings

Charge and spin order driven by Fermi surface nesting in weak to intermediate coupling.

Large Hund's coupling needed for observed magnetic and charge order in strongly correlated regime.

Quantum confinement significantly alters magnetic ordering and transport in ultra-thin slabs.

Abstract

Motivated by recent Fermi surface and transport measurements on LaNiO3, we study the Mott Metal-Insulator transitions of perovskite nickelates, with the chemical formula RNiO3, where R is a rare-earth ion. We introduce and study a minimal two-band model, which takes into account only the eg bands. In the weak to intermediate correlation limit, a Hartree-Fock analysis predicts charge and spin order consistent with experiments on R=Pr, Nd, driven by Fermi surface nesting. It also produces an interesting semi-metallic electronic state in the model when an ideal cubic structure is assumed. We also study the model in the strong interaction limit, and find that the charge and magnetic order observed in experiment exist only in the presence of very large Hund's coupling, suggesting that additional physics is required to explain the properties of the more insulating nickelates, R=Eu,Lu,Y. Next, we extend our analysis to slabs of finite thickness. In ultra-thin slabs, quantum confinement effects substantially change the nesting properties and the magnetic ordering of the bulk, driving the material to exhibit highly anisotropic transport properties. However, pure confinement alone does not significantly enhance insulating behavior. Based on these results, we discuss the importance of various physical effects, and propose some experiments.