Charge density waves and Fermi level pinning in monolayer and bilayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>SnSe</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
Shu-Ze Wang, Yimin Zhang, Jia-Qi Fan, Mingqiang Ren, Can‐Li Song, Xu-Cun Ma, Qi‐Kun Xue
Abstract
Materials with reduced dimensionality often exhibit exceptional properties that are different from their bulk counterparts. Here, we report the emergence of a commensurate $2\ifmmode\times\else\texttimes\fi{}2$ charge density wave (CDW) in monolayer and bilayer ${\mathrm{SnSe}}_{2}$ films by scanning tunneling microscopy. The visualized spatial modulation of the CDW phase becomes prominent near the Fermi level, which is pinned inside the semiconductor band gap of ${\mathrm{SnSe}}_{2}$. We show that both CDW and Fermi level pinning are intimately correlated with band bending and virtual induced gap states at the semiconductor heterointerface. Through interface engineering, the electron-density-dependent phase diagram is established in ${\mathrm{SnSe}}_{2}$. Fermi surface nesting between symmetry inequivalent electron pockets is revealed to drive the CDW formation and to provide an alternative CDW mechanism that might work in other compounds.