Molecular Mott state in the deficient spinel GaV$_4$S$_8$

TL;DR

This paper theoretically investigates the Mott-insulating phase of GaV$_4$S$_8$, revealing that molecular orbital effects due to tetrahedral clustering are crucial for understanding its electronic and structural properties, with multi-MO correlations and Hund's coupling being essential.

Contribution

It introduces a cluster extension of charge self-consistent embedded dynamical mean-field theory to study the MO-based Mott phase in GaV$_4$S$_8$, highlighting the importance of multi-MO correlations and Hund's coupling.

Findings

Molecular orbital picture is essential for describing the Mott phase.

Single MO truncation overemphasizes clustering tendencies.

Including Hund's coupling aligns theoretical structure with experiments.

Abstract

In this study, we investigated theoretically the Mott-insulating phase of a deficient spinel chalcogenide GaV$_4$S$_8$, which is known to form a tetrahedral V$_4$S$_4$ cluster unit that results in molecular orbitals (MOs) with a narrow bandwidth in the noninteracting limit. We used a cluster extension of charge self-consistent embedded dynamical mean-field theory to study the impact of strong intra-cluster correlations on the spectral properties as well as the structural degrees of freedom of the system. We found that the strong tetrahedral clustering renders the atomic Mott picture ineffective, and that the resulting MO picture is essential to describe the Mott phase. It was also found that, while the spectral properties can be qualitatively described by the truncation of the Hilbert space down to the lowest-energy MO, a proper description of the structural degrees of freedom requires the inclusion of multi-MO correlations that span a larger energy window. Specifically, we found that the lowest-energy MO description overemphasizes the clustering tendency, while the inclusion of the Hund's coupling between the lower- and higher-energy MOs corrects this tendency, bringing the theoretically predicted crystal structure into good agreement with the experiment.