Control of electric properties of silicene heterostructure by reversal of ferroelectric polarization

Abstract

Silicene is a kind of two-dimensional material composed of a honeycomb arrangement of silicon atoms. Compared with the structure of graphene, the buckled structure of silicene weakens the <inline-formula><tex-math id="M5">\begin{document}$\pi—\pi$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M5.png"/></alternatives></inline-formula> overlaps and turns the hybrid orbitals from <inline-formula><tex-math id="M6">\begin{document}$\rm sp^2$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M6.png"/></alternatives></inline-formula> to <inline-formula><tex-math id="M7">\begin{document}$\rm sp^3$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M7.png"/></alternatives></inline-formula>, which enhances the spin-orbit coupling strength but still preserves the Dirac cone near <i>K</i> or <i>K</i><i>'</i>. Owing to its buckled structure, silicene is susceptible to external parameters like electric field and substrate, which draws lots of attention both experimentally and theoretically. Recent progress of ferroelectricity in two-dimensional (2D) van der Waals materials found that the spontaneous ferroelectric polarization can be preserved even above room temperature, which inspires us to investigate how to tune the electric properties of silicene through the spontaneous polarization field of 2D ferroelectric substrate. <inline-formula><tex-math id="M8">\begin{document}${\rm In_{2}}X_3$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M8.png"/></alternatives></inline-formula> (<i>X</i> = Se,S,Te) Family recently were found to have single ferroelectric monolayers with reversible spontaneous electric polarization in both out-of-plane and in-plane orientations, and the lattice mismatch between silicene and <inline-formula><tex-math id="M9">\begin{document}$\rm In_{2}S_3$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M9.png"/></alternatives></inline-formula>is negligible. Therefore, we investigate the stacking and electric properties of silicene and monolayer <inline-formula><tex-math id="M10">\begin{document}$\rm In_{2}S_3$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M10.png"/></alternatives></inline-formula> heterostructure by the first-principles calculations. The spontaneous polarization field of <inline-formula><tex-math id="M11">\begin{document}$\rm In_{2}S_3$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M11.png"/></alternatives></inline-formula> is calculated to be 1.26 <inline-formula><tex-math id="M12">\begin{document}$\rm μC {\cdot} cm^{-2}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M12.png"/></alternatives></inline-formula>, comparable to the experimental results of <inline-formula><tex-math id="M13">\begin{document}$\rm In_{2}Se_3$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M13.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M13.png"/></alternatives></inline-formula>. We compare the different stacking order between silicene and <inline-formula><tex-math id="M14">\begin{document}$\rm In_{2}S_3$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M14.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M14.png"/></alternatives></inline-formula>. The calculated results shown that the <i>AB</i> stacking is the ground state stacking order, and the reversal of the ferroelectric polarization could tune the band structure of heterostructure. When the polarization direction of <inline-formula><tex-math id="M15">\begin{document}$\rm In_{2}S_3$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M15.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M15.png"/></alternatives></inline-formula> is upward, the layer distance between silicene and <inline-formula><tex-math id="M16">\begin{document}$\rm In_{2}S_3$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M16.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220815_M16.png"/></alternatives></inline-formula> is 3.93 Å, the polarization field and substrate interaction together break the<i> AB</i> sublattice symmetry and induce a 1.8 meV band gap near the Dirac point of <i>K</i> and <i>K'</i>, while the Berry curvature around <i>K </i>and <i>K' </i>have opposite signs, corresponding to valley Hall effect. When the polarization is downward, the layer distance decreases to 3.62 Å and the band gap around <i>K</i> and<i> K'</i> both increase to 30.8 meV. At the same time a 0.04<i>e</i> charge transfer makes some bands move across the Fermi energy, corresponding to metal state. Our results pave the way for studying the ferroelectric tuning silicene heterostructures and their potential applications in information industry.