Rutgers Center for Emergent Materials, Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA.
Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Nat Commun. 2016 May 24;7:11602. doi: 10.1038/ncomms11602.
Charged polar interfaces such as charged ferroelectric walls or heterostructured interfaces of ZnO/(Zn,Mg)O and LaAlO3/SrTiO3, across which the normal component of electric polarization changes suddenly, can host large two-dimensional conduction. Charged ferroelectric walls, which are energetically unfavourable in general, were found to be mysteriously abundant in hybrid improper ferroelectric (Ca,Sr)3Ti2O7 crystals. From the exploration of antiphase boundaries in bilayer-perovskites, here we discover that each of four polarization-direction states is degenerate with two antiphase domains, and these eight structural variants form a Z4 × Z2 domain structure with Z3 vortices and five distinct types of domain walls, whose topology is directly relevant to the presence of abundant charged walls. We also discover a zipper-like nature of antiphase boundaries, which are the reversible creation/annihilation centres of pairs of two types of ferroelectric walls (and also Z3-vortex pairs) in 90° and 180° polarization switching. Our results demonstrate the unexpectedly rich nature of hybrid improper ferroelectricity.
带电极性界面，如带有电荷的铁电壁或 ZnO/(Zn,Mg)O 和 LaAlO3/SrTiO3 的异质结构界面，其电极化的法向分量突然变化，可容纳大二维导通。在能量上通常不利的带电铁电壁在混合赝钙钛矿 (Ca,Sr)3Ti2O7 晶体中却神秘地大量存在。从双层钙钛矿的反相畴研究中，我们发现四个极化方向状态的每一个都与两个反相畴简并，这八个结构变体形成一个 Z4×Z2 畴结构，其中有 Z3 涡旋和五种不同类型的畴壁，其拓扑结构与大量带电壁的存在直接相关。我们还发现了反相畴的拉链状性质，在 90°和 180°极化翻转中，反相畴是两种铁电壁（以及 Z3-涡旋对）对的可逆生成/湮灭中心。我们的研究结果表明，混合赝钙钛矿的性质出人意料地丰富。
