La2CuO4 +y中局域晶格畸变的最佳不均匀性
Optimum inhomogeneity of local lattice distortions in La2CuO4+y
摘要：
从硅到过渡金属氧化物的材料中的电子功能在很大程度上受缺陷及其相对排列的控制。突出的例子是铜的氧化物，其中缺陷顺序与它们的高超导转变温度相关。即使在“最佳”超导样品中，氧缺陷序也可能是高度不均匀的，这就提出了样品区域的性质问题，在这些区域中，氧缺陷序不存在，但仍然形成了将有序区域结合在一起的“胶水”。在这里，我们使用扫描X射线显微衍射（光束直径为300 nm）表明，对于La2CuO4+y，“胶水”区域包含不相称的调制局部晶格畸变，其空间范围是最明显的最好的超导样品。对于一个欠掺杂的单晶与移动的氧原子在间隔层La2O2+y层插入之间的CuO 2层，无公度调制的局部晶格畸变形成液滴的有序的氧原子，其空间范围是最明显的最好的超导样品。因此，在这种最简单的高温超导体中，存在不是一个而是两个有序缺陷网络，它们可以被调整以实现最佳的超导性。对于一个给定的化学计量，最高的转变温度时，获得有序的氧和晶格缺陷形成分形图案，而不是出现在孤立的斑点。我们推测，材料的复杂性和超导转变温度Tc之间的关系实际上是由Tc和有序的缺陷网络的材料支持的分布之间的基本关系。
英文摘要：
Electronic functionalities in materials from silicon to transition metal oxides are to a large extent controlled by defects and their relative arrangement. Outstanding examples are the oxides of copper, where defect order is correlated with their high superconducting transition temperatures. The oxygen defect order can be highly inhomogeneous, even in "optimal" superconducting samples, which raises the question of the nature of the sample regions where the order does not exist but which nonetheless form the "glue" binding the ordered regions together. Here we use scanning X-ray microdiffraction (with beam 300 nm in diameter) to show that for La2CuO4+y, the "glue" regions contain incommensurate modulated local lattice distortions, whose spatial extent is most pronounced for the best superconducting samples. For an underdoped single crystal with mobile oxygen interstitials in the spacer La2O2+y layers intercalated between the CuO2 layers, the incommensurate modulated local lattice distortions form droplets anticorrelated with the ordered oxygen interstitials, and whose spatial extent is most pronounced for the best superconducting samples. In this simplest of high temperature superconductors, there are therefore not one, but two networks of ordered defects which can be tuned to achieve optimal superconductivity. For a given stoichiometry, the highest transition temperature is obtained when both the ordered oxygen and lattice defects form fractal patterns, as opposed to appearing in isolated spots. We speculate that the relationship between material complexity and superconducting transition temperature Tc is actually underpinned by a fundamental relation between Tc and the distribution of ordered defect networks supported by the materials.
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