Wannier States of FCC Symmetry Qualifying Paramagnetic NiO to Be a Mott Insulator

Ekkehard Krüger

doi:10.3390/sym12050687

Abstract

This letter extends my recent paper on antiferromagnetic NiO [Structural Distortion Stabilizing the Antiferromagnetic and Insulating Ground State of NiO, Symmetry 2020, 12(1), 56] by including also the paramagnetic phase of this compound. I report evidence that paramagnetic NiO possesses a narrow, roughly half-filled energy band that produces a nonadiabatic atomic-like motion providing the basis for a Mott insulator in the paramagnetic phase. While the atomic-like motion operating in the antiferromagnetic phase is adapted to the symmetry of the antiferromagnetic state, in the paramagnetic phase, the related localized states are represented by optimally localized Wannier functions possessing the full fcc symmetry of paramagnetic NiO. The nonadiabatic Wannier states are twofold degenerate, have d-like symmetry, and are situated at the Ni atoms.

Highlights

In my previous paper [1] on NiO, I reported evidence that the structural distortion of antiferromagnetic NiO stabilizes the antiferromagnetic and insulating ground state of this compound. This state is enabled by the nonadiabatic atomic-like motion of the electrons in the “magnetic super band” defined within the nonadiabatic Heisenberg model (NHM) [1]
In view of my observation that the nonadiabatic atomic-like motion defined within the NHM is responsible for the insulating ground states of antiferromagnetic BaMn2 As2 and antiferromagnetic
Any atomic-like motion as defined within the NHM is represented by optimally localized symmetry-adapted Wannier function being an exact unitary transformation of the Bloch functions of a narrow, roughly half-filled energy band [1]

Summary

Introduction

In my previous paper [1] on NiO, I reported evidence that the structural distortion of antiferromagnetic NiO stabilizes the antiferromagnetic and insulating ground state of this compound. This state is enabled by the nonadiabatic atomic-like motion of the electrons in the “magnetic super band” defined within the nonadiabatic Heisenberg model (NHM) [1]. Because this atomic-like motion only exists in the space group of the antiferromagnetic phase, paramagnetic NiO should be metallic.

Nonadiabatic Atomic-Like Motion in Paramagnetic NiO

Discussion

Paramagnetic NiO

Conclusions