Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-3800, USA.
Phys Rev Lett. 2012 Aug 10;109(6):067601. doi: 10.1103/PhysRevLett.109.067601. Epub 2012 Aug 9.
We have fabricated PbTiO3/SrRuO3 superlattices with ultrathin SrRuO3 layers. Because of the superlattice geometry, the samples show a large anisotropy in their electrical resistivity, which can be controlled by changing the thickness of the PbTiO3 layers. Therefore, along the ferroelectric direction, SrRuO3 layers can act as dielectric, rather than metallic, elements. We show that, by reducing the concentration of PbTiO3, an increasingly important effect of polarization asymmetry due to compositional inversion symmetry breaking occurs. The results are significant as they represent a new class of ferroelectric superlattices, with a rich and complex phase diagram. By expanding our set of materials we are able to introduce new behaviors that can only occur when one of the materials is not a perovskite titanate. Here, compositional inversion symmetry breaking in bicolor superlattices, due to the combined variation of A and B site ions within the superlattice, is demonstrated using a combination of experimental measurements and first principles density functional theory.
我们已经制造了具有超薄 SrRuO3 层的 PbTiO3/SrRuO3 超晶格。由于超晶格的几何形状，样品在其电阻率方面表现出很大的各向异性，这可以通过改变 PbTiO3 层的厚度来控制。因此，沿着铁电方向，SrRuO3 层可以充当介电而不是金属元素。我们表明，通过降低 PbTiO3 的浓度，由于组成反转对称性破坏而导致的极化非对称性的影响变得越来越重要。这些结果意义重大，因为它们代表了一类新的铁电超晶格，具有丰富而复杂的相图。通过扩展我们的材料集，我们能够引入只有当其中一种材料不是钙钛矿钛酸盐时才会出现的新行为。在这里，通过实验测量和第一性原理密度泛函理论的结合，证明了双色超晶格中由于超晶格中 A 和 B 位离子的组合变化而导致的组成反转对称性破坏。
