Electronic Structure of NiO: Antiferromagnetic Transition and Photoelectron Spectra in the Ordered Phase

TL;DR

This study investigates the antiferromagnetic transition and photoelectron spectra of NiO using the Variational Cluster Approximation, achieving good agreement with experimental data and revealing key electronic features.

Contribution

The paper applies the Variational Cluster Approximation with realistic parameters to accurately model NiO's magnetic transition and spectral properties, highlighting the role of electron hopping and multiplet effects.

Findings

Calculated Neel temperature of 481 K closely matches experimental 523 K.

Good agreement between calculated and experimental photoelectron spectra, including flat bands.

Predicted a 10% increase in the insulating gap above the transition temperature.

Abstract

The thermodynamics of the antiferromagnetic ordering transition in NiO and the photoelectron spectra in the antiferromagnetic phase are studied by the Variational Cluster Approximation. Using realistic Racah parameters to describe the Coulomb interaction in the Ni 3d shell and a Slater-Koster parameter pds which is slightly (10%) increased over the band structure estimate the calculated Neel temperature is 481 Kelvin (experimental value: 523 Kelvin). The magnetic susceptibility above TN has Curie-Weiss form. A significant contribution to the stabilization of the antiferromagnetic phase comes from electron hopping between oxygen which would be missed in theories that consider superexchange along a single bond only. The single particle spectral function in the ordered phase is in good agreement with experiment, in particular a number of dispersionless bands which are not reproduced by most calculations are obtained correctly. These flat bands are shown to be direct experimental evidence for a dispersionless electronic self-energy with several poles in the energy range of the valence band which originate from the multiplets of the Ni3+ ion. Small but possibly experimentally detectable changes of the photoelectron spectra with temperature are discussed, in p articular a widening of the insulating gap in the paramagnetic phase by approximately 10% is predicted.