铁电极化翻转对硅烯异质结中电子性质的调控

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

硅烯是硅原子蜂窝状排列构成的二维材料,由于其层内硅原子不在同一平面上而易受到电场等调控,近年来成为理论和实验研究的一个热点.借助于第一性原理计算方法,详细研究了硅烯和二维铁电材料In_(2)S_(3)单层材料异质结的堆垛形式和电子结构.计算结果表明,硅烯和In_(2)S_(3)可以形成稳定的异质结,In_(2)S_(3)衬底的自发铁电极化对硅烯能带有显著调控作用.铁电极化方向向上时,自发极化电场和衬底的共同作用在狄拉克点打开能隙,K和K’点贝利曲率符号相反,对应能谷霍尔效应态.铁电极化方向向下时,硅烯和In_(2)S_(3)之间间距变小,费米能级有能带穿过,对应金属态.研究结果对铁电调控硅烯二维异质结提供参考,为硅烯异质结在信息存储领域的应用指明方向.

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 theπ—πoverlaps and turns the hybrid orbitals from sp^(2) to sp^(3),which enhances the spin-orbit coupling strength but still preserves the Dirac cone near K or K’.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(2 D)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 2 D ferroelectric substrate.In_(2)X_(3)(X=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 In_(2)S_(3) is negligible.Therefore,we investigate the stacking and electric properties of silicene and monolayer In_(2)S_(3) heterostructure by the first-principles calculations.The spontaneous polarization field of In_(2)S_(3) is calculated to be 1.26μC·cm^(-2),comparable to the experimental results of In_(2)Se_(3).We compare the different stacking order between silicene and In_(2)S_(3).The calculated results shown that the AB 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 In_(2)S_(3) is upward,the layer distance between silicene and In_(2)S_(3) is 3.93A,the polarization field and substrate interaction together break the AB sub lattice symmetry and induce a 1.8 meV band gap near the Dirac point of K and K’,while the Berry curvature around K and K’have opposite signs,corresponding to valley Hall effect.When the polarization is downward,the layer distance decreases to 3.62?and the band gap around K and K’both increase to 30.8 meV.At the same time a 0.04 e 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.