Temperature driven Vanadium clusterization and band gap enlargement in the layered misfit compound (LaS)$_{1.196}$VS$_2$

TL;DR

This study investigates how temperature influences the electronic and structural properties of (LaS)$_{1.196}$VS$_2$, revealing that structural distortions and vanadium clusterization drive the transition from metallic to insulating states, challenging previous assumptions about electronic correlations.

Contribution

The paper demonstrates that structural distortions and vanadium clusterization, rather than electronic correlations, are key to the insulating behavior in (LaS)$_{1.196}$VS$_2$, providing new insights into its electronic properties.

Findings

Spectral weight transfer up to 1 eV observed with optical and photoemission spectroscopy.

Band structure changes from metallic-like at 300K to insulating at low temperature.

Structural distortions and vanadium clusterization increase as temperature decreases.

Abstract

Intriguing properties of the misfit layered chalcogenide (LaS)$_{1.196}$VS$_2$ crystals were investigated by transport, optical measurements, angle-resolved photoemission (ARPES) and x-ray diffraction. Although no clear anomaly is found in transport properties as a function of temperature, a large spectral weight transfer, up to at least 1 eV, is observed by both optical and photoemission spectroscopies. ARPES reveals that a nearly filled band with negative curvature, close enough from the Fermi level at 300K to produce metallic-like behaviour as observed in optical conductivity spectra. At low temperature, the band structure is strongly modified, yielding to an insulating state with a optical gap of 120 meV. An accurate (3+1)D analysis of x-ray diffraction data shows that, although a phase transition does not occur, structural distortions increase as temperature is decreased, and vanadium clusterization is enhanced. We found that the changes of electronic properties and structure are intimately related. This indicates that structural distorsion play a major role in the insulating nature of (LaS)$_{1.196}$VS$_2$ and that electronic correlation may not be important, contrary to previous belief. These results shed a new light on the mechanism at the origin of non-linear electric properties observed in (LaS)$_{1.196}$VS$_2$.