Roles of the Narrow Electronic Band near the Fermi Level in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>1</mml:mn><mml:mi>T</mml:mi><mml:mtext>−</mml:mtext><mml:msub><mml:mrow><mml:mi>TaS</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>-Related Layered Materials
Chenhaoping Wen, Jingjing Gao, Yuan Xie, Qing Zhang, Pengfei Kong, Jinghui Wang, Yilan Jiang, Xuan Luo, Jun Li, W. J. Lu, Yuping Sun, Shichao Yan
Abstract
Here we use low-temperature scanning tunneling microscopy and spectroscopy to reveal the roles of the narrow electronic band in two $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$-related materials (bulk $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ and $4{H}_{\mathrm{b}}\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$). $4{H}_{\mathrm{b}}\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ is a superconducting compound with alternating $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ and $1H\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ layers, where the $1H\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ layer has a weak charge density wave (CDW) pattern and reduces the CDW coupling between the adjacent $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ layers. In the $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ layer of $4{H}_{\mathrm{b}}\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$, we observe a narrow electronic band located near the Fermi level, and its spatial distribution is consistent with the tight-binding calculations for two-dimensional $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ layers. The weak electronic hybridization between the $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ and $1H\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ layers in $4{H}_{\mathrm{b}}\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ shifts the narrow electronic band to be slightly above the Fermi level, which suppresses the electronic correlation-induced band splitting. In contrast, in bulk $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$, there is an interlayer CDW coupling-induced insulating gap. In comparison with the spatial distributions of the electronic states in bulk $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ and $4{H}_{\mathrm{b}}\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$, the insulating gap in bulk $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ results from the formation of a bonding band and an antibonding band due to the overlap of the narrow electronic bands in the dimerized $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ layers.