晶体中不可约铁电性的直接可视化
Direct Visualization of Irreducible Ferrielectricity in Crystals
摘要：
在固体中，电荷极性可以与自旋极性一一对应，如铁电性/铁磁性、反铁电性/反铁磁性，甚至偶极涡旋/磁涡旋，但亚铁电性/亚铁磁性在微观层次上却一直是一个截然不同的故事。由于电荷偶极的定义涉及多个离子，因此偶极单元可以有多种选择，这使得大多数铁电性阶数等效于铁电性阶数，即这种铁电性不一定是真正独立的极性分支。在这项工作中，通过使用球面像差校正的扫描透射电子显微镜，我们可视化了一个非平凡的铁电结构的演变BaFe 2 Se 3，其中两个极性子晶格的发展是不同步的，我们称之为不可约铁电性。这种不可约的铁电性导致了非单调的行为的温度依赖的极化，甚至在有序状态的补偿点。我们的发现明确区分了铁电体和铁电体。
英文摘要：
In solids, charge polarity can one-to-one correspond to spin polarity phenomenologically, e.g. ferroelectricity/ferromagnetism, antiferroelectricity/antiferromagnetism, and even dipole-vortex/magnetic-vortex, but ferrielectricity/ferrimagnetism kept telling a disparate story in microscopic level. Since the definition of a charge dipole involves more than one ion, there may be multiple choices for a dipole unit, which makes most ferrielectric orders equivalent to ferroelectric ones, i.e. this ferrielectricity is not necessary to be a real independent branch of polarity. In this work, by using the spherical aberration-corrected scanning transmission electron microscope, we visualize a nontrivial ferrielectric structural evolution in BaFe2Se3, in which the development of two polar sub-lattices is out-of-sync, for which we term it as irreducible ferrielectricity. Such irreducible ferrielectricity leads to a non-monotonic behavior for the temperature-dependent polarization, and even a compensation point in the ordered state. Our finding unambiguously distinguishes ferrielectrics from ferroelectrics in solids.
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