npj: 铁电体调控—扭转力改变极化
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铁电纳米材料中电偶极子因为受限于维度会形成涡旋结构。与传统的铁电畴结构相比，铁电涡旋态的自身特性及其对外场的耦合均具有显著不同的特点，在基础理论研究及器件研发方面具有巨大的潜在价值，近十年来，引起了人们极大的兴趣。然而，目前对于如何控制和应用铁电涡旋态仍缺乏有效方案。
来自中国中山大学的郑跃教授领导的研究团队，一直致力于力电载荷对于铁电涡旋态稳定和转变机理以及相关特性影响规律的研究。近期，他们基于热力学理论及利用基于第一性原理的计算机模拟，对(BaTiO3)m(SrTiO3)n铁电/顺电复合纳米线进行了系统研究，找到了一种可有效调控铁电纳米线中极化-涡旋共存态的方案。他们提出，在铁电纳米线中，通过结合均匀电场和扭矩，可以实现极化-涡旋共存态的调控。这种方案的理论基础来源于该纳米线中存在的极化、涡矩和扭转力之间的三线性耦合。模拟结果发现，通过翻转铁电纳米线轴向极化，可以实现其涡旋手性的翻转，且翻转涡旋手性所需的电场和扭矩均很小。他们同时指出，该方案也可以用于铁电斯格明子态、铁电纳米点中涡旋态的调控。该研究为利用剪切应力应变工程来调控和设计基于奇异电偶极态的铁电器件提供了可能。
该文近期发表于npj Computational Materials 4: 78 (2018)，英文标题与摘要如下，点击左下角“阅读原文”可以自由获取论文PDF。
Controlling polar-toroidal multi-order states in twisted ferroelectric nanowires
Jianyi Liu, Ye Ji, Shuai Yuan, Lili Ding, Weijin Chen & Yue Zheng
The toroidal order of electric dipoles in ferroelectric materials has attracted attention in the past decade due to fascinating properties and great potential for enabling novel memory devices, and functional devices in general. However, facile manipulation of toroidal order in ferroelectrics remains challenging. Here, using first-principles derived simulations, we demonstrate an efficient scheme to control the polar-toroidal multi-order (PTMO) states in ferroelectric nanowires. Two feasible strategies of controlling PTMO states by a combination of homogeneous electric field and torque are carried out in ferroelectric/paraelectric composite nanowires. This is possible based on trilinear coupling between polarization, toroidization and the twist force. As a result, switching of the toroidization of the nanowire can be readily achieved by reversal of the axial polarization. The torque threshold needed to control PTMO states is also calculated and found to be relatively small, indicating the feasibility of this method. Our study demonstrates facile control of PTMO states, including ferroelectric skyrmions, in ferroelectrics and is a step towards designing ferroelectric devices based on multi-order states.
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