Linear behavior of the optical conductivity and incoherent charge transport in BaCoS2

TL;DR

This study reveals that BaCoS2 exhibits linear optical conductivity over a broad spectrum, with incoherent charge transport driven by electronic correlations, indicating a non-Fermi liquid Hund's metal state rather than a Mott insulator.

Contribution

The paper combines experimental optical measurements with ab initio dynamical mean field theory to explain the linear conductivity and incoherent transport in BaCoS2 as a Hund's metal near an incipient Mott phase.

Findings

Linear optical conductivity observed over broad spectral range.

Absence of a gap in the paramagnetic phase above 300 K.

Incoherent charge transport linked to electronic correlations.

Abstract

Optical conductivity measurements on a BaCoS2 single crystal show an unusual linear behavior over a broad spectral range. In the paramagnetic phase above 300 K, the spectrum shows no gap, which contradicts the previously proposed scenario of a charge-transfer Mott insulator. Ab initio dynamical mean field theory calculations including a retarded Hubbard interaction explain the data in terms of an incipient opening of a Co(3d)-S(3p) charge-transfer gap concomitant to incoherent charge transport driven by electronic correlations. These results point to a non-Fermi liquid scenario with Hund's metal properties in the paramagnetic state, which arises from an incipient Mott phase destabilized by low-energy charge fluctuations across the vanishing 3d-3p charge-transfer gap.