Roles of the Narrow Electronic Band near the Fermi Level in 1T-TaS2-Related Layered Materials
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-TaS2-related materials (bulk 1T-TaS2 and 4Hb-TaS2). 4Hb-TaS2 is a superconducting compound with alternating 1T-TaS2 and 1H-TaS2 layers, where the 1H-TaS2 layer has weak charge density wave (CDW) pattern and reduces the CDW coupling between the adjacent 1T-TaS2 layers. In the 1T-TaS2 layer of 4Hb-TaS2, 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-TaS2 layers. The weak electronic hybridization between the 1T-TaS2 and 1H-TaS2 layers in 4Hb-TaS2 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-TaS2, there is an interlayer CDW coupling induced insulating gap. In comparison with the spatial distributions of the electronic states in bulk 1T-TaS2 and 4Hb-TaS2, the insulating gap in bulk 1T-TaS2 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-TaS2 layers.
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