Optical signature for distinguishing between Mott-Hubbard, intermediate and charge-transfer insulators

TL;DR

This study demonstrates that optical absorption spectra can serve as a clear fingerprint to distinguish between different types of insulators in transition-metal compounds, specifically in CoO, using first-principles calculations.

Contribution

The paper introduces a novel approach to identify insulator types via optical spectra, providing a practical experimental method that improves upon existing theoretical interpretation techniques.

Findings

Optical absorption spectra reveal qualitative differences in peak satellites.

CoO is identified as an intermediate insulator, not a Mott-Hubbard insulator.

The method distinguishes insulator types without additional theoretical analysis.

Abstract

Determining the nature of band gaps in transition-metal compounds remains challenging. We present a first-principles study on electronic and optical properties of CoO using hybrid functional pseudopotentials. We show that optical absorption spectrum can provide a clear fingerprint to distinguish between Mott-Hubbard, intermediate and charge-transfer insulators. This discrimination is reflected by the qualitative difference in peak satellites due to unique interplay between $d$-$d$ and $p$-$d$ excitations, thus allowing identification from experimental data alone, unlike the existing methods that require additional theoretical interpretation. We conclude that the CoO is an intermediate, rather than a Mott-Hubbard insulator as is initially believed.