The family of layered thio- and seleno-phosphates has gained attention as potential control dielectrics for the rapidly growing family of two-dimensional and quasi-two-dimensional electronic materials. Here we report a combination of density functional theory calculations, quantum molecular dynamics simulations and variable-temperature, -pressure and -bias piezoresponse force microscopy data to predict and verify the existence of an unusual ferroelectric property-a uniaxial quadruple potential well for Cu displacements-enabled by the van der Waals gap in copper indium thiophosphate (CuInP2S6). The calculated potential energy landscape for Cu displacements is strongly influenced by strain, accounting for the origin of the negative piezoelectric coefficient and rendering CuInP2S6 a rare example of a uniaxial multi-well ferroelectric. Experimental data verify the coexistence of four polarization states and explore the temperature-, pressure- and bias-dependent piezoelectric and ferroelectric properties, which are supported by bias-dependent molecular dynamics simulations. These phenomena offer new opportunities for both fundamental studies and applications in data storage and electronics.

中文翻译：

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可调四阱铁电范德华晶体。

层状硫代磷酸盐和硒磷酸盐家族作为快速增长的二维和准二维电子材料家族的潜在控制电介质而受到关注。在这里，我们报告了密度泛函理论计算、量子分子动力学模拟和可变温度、压力和偏置压电响应力显微镜数据的组合，以预测和验证不寻常的铁电特性的存在 - 用于 Cu 位移的单轴四重势阱 -通过硫代磷酸铜铟 (CuInP2S6) 中的范德华间隙实现。计算出的 Cu 位移的势能景观受应变的强烈影响，解释了负压电系数的起源，并使 CuInP2S6 成为单轴多孔铁电体的罕见例子。实验数据验证了四种极化状态的共存，并探索了依赖于偏压的分子动力学模拟支持的温度、压力和偏压相关的压电和铁电特性。这些现象为数据存储和电子领域的基础研究和应用提供了新的机会。