Roles of the Narrow Electronic Band near the Fermi Level in 1T-TaS$_2$-Related Layered Materials

TL;DR

This study uses STM/STS to investigate the narrow electronic band near the Fermi level in 1T-TaS$_2$-related layered materials, revealing its role in electronic properties and differences between bulk and layered compounds.

Contribution

It provides detailed experimental insights into how the narrow electronic band influences electronic correlations and interlayer coupling in 1T-TaS$_2$-related materials.

Findings

Narrow electronic band near Fermi level observed in 4Hb-TaS$_2$

Weak hybridization shifts the band above Fermi level in 4Hb-TaS$_2$

Insulating gap in bulk 1T-TaS$_2$ results from interlayer CDW coupling

Abstract

Here we use low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) to reveal the roles of the narrow electronic band in two 1T-TaS$_2$-related materials (bulk 1T-TaS$_2$ and 4Hb-TaS$_2$). 4Hb-TaS$_2$ is a superconducting compound with alternating 1T-TaS$_2$ and 1H-TaS$_2$ layers, where the 1H-TaS$_2$ layer has weak charge density wave (CDW) pattern and reduces the CDW coupling between the adjacent 1T-TaS$_2$ layers. In the 1T-TaS$_2$ layer of 4Hb-TaS$_2$, we observe a narrow electronic band located near Fermi level, and its spatial distribution is consistent with the tight-binding calculations for two-dimensional 1T-TaS$_2$ layers. The weak electronic hybridization between the 1T-TaS$_2$ and 1H-TaS$_2$ layers in 4Hb-TaS$_2$ shifts the narrow electronic band to be slightly above the Fermi level, which suppresses the electronic correlation induced band splitting. In contrast, in bulk 1T-TaS$_2$, there is an interlayer CDW coupling induced insulating gap. In comparison with the spatial distributions of the electronic states in bulk 1T-TaS$_2$ and 4Hb-TaS$_2$, the insulating gap in bulk 1T-TaS$_2$ results from the formation of a bonding band and an antibonding band due to the overlap of the narrow electronic bands in the dimerized 1T-TaS$_2$ layers.