Local correlations, non-local screening, multiplets, and band formation in NiO

TL;DR

This study compares the electronic structure of NiO in bulk and impurity forms, revealing complex screening and correlation effects that influence its valence band properties and complicate the observation of band dispersions.

Contribution

It provides a detailed analysis of local and non-local screening processes in NiO, establishing the nature of its ionization states and the impact on valence band features.

Findings

Pronounced satellite features in NiO's valence band.

Screening involves local quasi-core and non-local states.

Effective Ni 3d band width is approximately 0.25 eV.

Abstract

We report on a comparative study of the valence band electronic structure of NiO as bulk material and of NiO as impurity in MgO. From the impurity we have been able to determine reliably the parameters which describe the local correlations, thereby establishing the compensated-spin character of the first ionization state or the state created by hole doping. Using bulk-sensitive x-ray photoemission we identify pronounced satellite features in the valence band of bulk NiO which cannot be explained by single-site many body approaches nor by mean field calculations. We infer the presence of screening processes involving local quasi-core states in the valence band and non-local coherent many body states. These processes are strong and the propagation of an extra hole in the valence band of NiO will therefore be accompanied by a range of high energy excitations. This in turn will make the observation of the dispersion relations in the Ni 3d bands difficult, also because the effective band width is no more than 0.25 eV as estimated from multi-site calculations.