Recently, the presence of an out-of-plane ferroelectric polarization was experimentally confirmed in bilayer two-dimensional (2D) hexagonal boron nitride (h-BN). In this work, we employ first-principles computations to reveal that (i) such slidetronic ferroelectricity is electronic in nature and arises from in-plane interlayer translation, which is distinctive among 2D slidetronic ferroelectric materials; and (ii) there is a coexistence of a negative longitudinal piezoelectric effect and an out-of-plane negative Poisson's ratio in the ferroelectric state of bilayer h-BN, which we refer to as anomalous double-negative effects.

中文翻译：

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双层六方氮化硼中的异常铁电性和双负效应

最近，在双层二维（2D）六方氮化硼（h-BN）中实验证实了平面外铁电极化的存在。在这项工作中，我们采用第一性原理计算来揭示（i）这种滑动电子铁电性本质上是电子的，并且来自平面内层间平移，这在二维滑动电子铁电材料中是独特的；(ii) 在双层 h-BN 的铁电状态下，负纵向压电效应和面外负泊松比并存，我们称之为反常双负效应。