Effect of stacking order on the electronic state of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>1</mml:mn><mml:mi>T</mml:mi><mml:mtext>−</mml:mtext><mml:msub><mml:mi>TaS</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>
Zongxiu Wu, Kunliang Bu, Wenhao Zhang, Ying Fei, Yuan Zheng, Jingjing Gao, Xuan Luo, Zheng Liu, Yuping Sun, Yi Yin
Abstract
New theoretical proposals and experimental findings on transition metal dichalcogenide $1T\ensuremath{-}{\mathrm{TaS}}_{2}$ have revived interest in its possible Mott insulating state. We perform a comprehensive scanning tunneling microscopy and spectroscopy experiment on different single-step areas in pristine $1T\ensuremath{-}{\mathrm{TaS}}_{2}$. After accurately determining the relative displacement of the Star of David superlattices in two layers, we find that different stacking orders can correspond to a similar large-gap spectrum on the upper terrace. When the measurement is performed away from the step edge, the large-gap spectrum can always be maintained. The stacking order seems to rarely disturb the large-gap spectrum in the ideal bulk material. We conclude that the large insulating gap is from the single-layer property, which is a correlation-induced Mott gap based on the single-band Hubbard model. Specific stacking orders can perturb the state and induce a small-gap or metallic spectrum for a limited area around the step edge, which we attribute to a surface and edge phenomenon. Our work provides more evidence about the stacking-order effect on the electronic state and deepens our understanding of the Mott insulating state in $1T\ensuremath{-}{\mathrm{TaS}}_{2}$.