Two-dimensional van der Waals (vdW) ferroelectrics, renowned for their spontaneous breaking of inversion symmetry and finite electric polarization, are pivotal in nonlinear optics and low-power nanoelectronics. Prior studies primarily focused on materials exhibiting out-of-plane or in-plane ferroelectric polarization, whose rotational degrees of freedom are commonly overlooked. Herein, we experimentally validate the existence of a weak yet symmetry-allowed in-plane polarization in the low-symmetry vdW ferroelectric CuInP2S6 by rigorous structural analysis and vectorial property characterizations. Remarkably, the magnitude of this in-plane polarization is tunable via an interface-induced electric field, leading to a significant contrast in second harmonic generation between oppositely polarized domains. Based on this unique rotational capability of electric polarization, we demonstrate an electrically tunable second-order optical emission in a fabricated vdW ferroelectric capacitor. Our findings highlight the intricate interplay between crystal symmetry and tensorial physical properties, providing a novel pathway for manipulating nonlinear optical functionalities in vdW layered ferroelectrics.

中文翻译：

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范德华分层铁电 CuInP2S6 中二次谐波产生的极化-旋转驱动调制


二维范德华 （vdW） 铁电体以其自发打破反转对称性和有限极化而闻名，在非线性光学和低功率纳米电子学中发挥着关键作用。以前的研究主要集中在表现出面外或面内铁电极化的材料上，其旋转自由度通常被忽视。在此，我们通过严格的结构分析和矢量特性表征，实验验证了低对称性 vdW 铁电 CuInP2S6 中存在弱但对称允许的面内极化。值得注意的是，这种面内极化的大小可以通过界面感应电场进行调节，从而导致相反极化域之间的二次谐波产生显着对比。基于这种独特的电极化旋转能力，我们展示了在制造的 vdW 铁电电容器中的电可调二阶光发射。我们的研究结果强调了晶体对称性和张量物理性质之间错综复杂的相互作用，为操纵 vdW 层状铁电体中的非线性光学功能提供了一条新的途径。