Deb Swarup, Cao Wei, Raab Noam, Watanabe Kenji, Taniguchi Takashi, Goldstein Moshe, Kronik Leeor, Urbakh Michael, Hod Oded, Ben Shalom Moshe
School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel.
Department of Physical Chemistry, School of Chemistry, The Raymond and Beverly Sackler Faculty of Exact Sciences and The Sackler Center for Computational Molecular and Materials Science, Tel Aviv University, Tel Aviv, Israel.
Nature. 2022 Dec;612(7940):465-469. doi: 10.1038/s41586-022-05341-5. Epub 2022 Nov 9.
Ferroelectricity in atomically thin bilayer structures has been recently predicted and measured in two-dimensional materials with hexagonal non-centrosymmetric unit-cells. The crystal symmetry translates lateral shifts between parallel two-dimensional layers to sign changes in their out-of-plane electric polarization, a mechanism termed 'slide-tronics'. These observations have been restricted to switching between only two polarization states under low charge carrier densities, limiting the practical application of the revealed phenomena. To overcome these issues, one should explore the nature of polarization in multi-layered van der Waals stacks, how it is governed by intra- and interlayer charge redistribution and to what extent it survives the addition of mobile charge carriers. To explore these questions, we conduct surface potential measurements of parallel WSe and MoS multi-layers with aligned and anti-aligned configurations of the polar interfaces. We find evenly spaced, nearly decoupled potential steps, indicating highly confined interfacial electric fields that provide a means to design multi-state 'ladder-ferroelectrics'. Furthermore, we find that the internal polarization remains notable on electrostatic doping of mobile charge carrier densities as high as 10 cm, with substantial in-plane conductivity. Using density functional theory calculations, we trace the extra charge redistribution in real and momentum spaces and identify an eventual doping-induced depolarization mechanism.
原子级薄的双层结构中的铁电性最近已在具有六边形非中心对称晶胞的二维材料中得到预测和测量。晶体对称性将平行二维层之间的横向位移转化为其面外电极化的符号变化，这一机制被称为“滑动电子学”。这些观察结果仅限于在低载流子密度下仅在两种极化状态之间切换，限制了所揭示现象的实际应用。为了克服这些问题，人们应该探索多层范德华堆栈中极化的本质，它是如何由层内和层间电荷重新分布所控制的，以及在添加移动电荷载流子后它能在多大程度上得以保留。为了探究这些问题，我们对具有极化界面的对齐和反对齐配置的平行WSe和MoS多层进行了表面电势测量。我们发现了均匀间隔、几乎解耦的电势台阶，这表明存在高度受限的界面电场，为设计多态“阶梯铁电体”提供了一种方法。此外，我们发现，在高达10¹³ cm⁻²的移动电荷载流子密度的静电掺杂下，内部极化仍然显著，且具有可观的面内电导率。使用密度泛函理论计算，我们追踪了实空间和动量空间中的额外电荷重新分布，并确定了最终的掺杂诱导去极化机制。
