Electron Complexity Laboratory, Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, Heraklion 70013, Greece.
Nat Commun. 2012;3:1064. doi: 10.1038/ncomms2061.
Heterostructured material systems devoid of ferroic components are presumed not to display ordering associated with ferroelectricity. In heterostructures composed of transition metal oxides, however, the disruption introduced by an interface can affect the balance of the competing interactions among electronic spins, charges and orbitals. This has led to the emergence of properties absent in the original building blocks of a heterostructure, including metallicity, magnetism and superconductivity. Here we report the discovery of ferroelectricity in artificial tri-layer superlattices consisting solely of non-ferroelectric NdMnO(3)/SrMnO(3)/LaMnO(3) layers. Ferroelectricity was observed below 40 K exhibiting strong tunability by superlattice periodicity. Furthermore, magnetoelectric coupling resulted in 150% magnetic modulation of the polarization. Density functional calculations indicate that broken space inversion symmetry and mixed valency, because of cationic asymmetry and interfacial polar discontinuity, respectively, give rise to the observed behaviour. Our results demonstrate the engineering of asymmetric layered structures with emergent ferroelectric and magnetic field tunable functions distinct from that of normal devices, for which the components are typically ferroelectrics.
在没有铁电成分的杂化材料系统中，人们认为不会显示与铁电性相关的有序性。然而，在由过渡金属氧化物组成的杂结构中，界面引入的不连续性会影响电子自旋、电荷和轨道之间竞争相互作用的平衡。这导致了杂结构原始构建块中不存在的特性的出现，包括金属性、磁性和超导性。在这里，我们报告了仅由非铁电 NdMnO(3)/SrMnO(3)/LaMnO(3)层组成的人工三层超晶格中发现的铁电性。在低于 40 K 的温度下观察到铁电性，其超晶格周期性表现出很强的可调谐性。此外，磁电耦合导致极化的 150%磁调制。密度泛函计算表明，由于阳离子不对称和界面极性不连续性，空间反转对称性的破坏和混合价态分别导致了观察到的行为。我们的结果表明，可以通过工程设计不对称层状结构来实现铁电和磁场可调谐功能，这些功能与通常的器件不同，通常器件的组件是铁电体。
