Roles of the Narrow Electronic Band near the Fermi Level in 1T-TaS$_2$-Related Layered Materials (2103.06553v4)

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.