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X-ray diffuse scattering studies of the local structural inhomogeneities in high temperature superconductors.

机译：高温超导体中局部结构不均匀性的X射线扩散散射研究。

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摘要

The high temperature superconductivity in cuprates is realized by off-stoichiometric doping. In addition to contributing carriers to the CuO2 planes, the dopants inherently introduce local disorder into the systems. Using the X-ray diffuse scattering technique, we studied the dopant-induced local structural distortions in two cuprate compounds: La1.92Sr0.08CuO 4 and YBa2Cu3O6.92.;On La1.92Sr0.08CuO4, strong anisotropic diffuse scattering pattern on top of the diffuse scattering due to thermal vibrations was observed. Our quantitative analysis shows that the observed anisotropic X-ray diffuse scattering intensities can be well described by the Huang Diffuse Scattering (HDS) theory with the single defect approximation, which indicates the Sr dopants are randomly distributed in the crystal. Based on the fitted parameters, the Sr-dopant induced elastic lattice distortion pattern was reconstructed. The big amplitude of the elastic lattice distortion near the Sr dopants suggests that Sr-dopant induced local structural modulation might be the origin of the electronic inhomogeneities observed with scanning tunneling microscopy experiments.;The oxygen vacancies in YBa2Cu3O6.92 behave in a different way. Our X-ray diffuse scattering measurements reveal that majority of the oxygen vacancies tend to cluster together and are ordered to form a 4-unit-cell superstructure with q&ar;0 = (¼, 0, 0) along a* direction. The superlattice consists of large anisotropic displacements of Cu, Ba, and O atoms, respectively and appears to be consistent with the presence of an O-ordered "Ortho-IV" phase. These "Ortho-IV" minority phase islands also induce long-range strains to the surrounding lattices, which manifest themselves as HDS observed in our experiments. Our quantitative analysis further revealed a b direction lattice modulation within the islands with the wavevector to be q&ar;1 = (0, 0.21, 0). The fact that q&ar;1 is very close to the nesting vector connecting the nearly nested Fermi surface (FS) "ridges" originated from the metallic Cu-O chains strongly indicates that the b direction modulation is induced by the FS effect.
机译：铜盐中的高温超导性是通过非化学计量掺杂实现的。除了向CuO2平面贡献载流子外，掺杂剂还固有地将局部无序引入系统。使用X射线扩散散射技术，我们研究了两种铜酸盐化合物La1.92Sr0.08CuO 4和YBa2Cu3O6.92中掺杂剂引起的局部结构畸变;在La1.92Sr0.08CuO4上，强掺杂各向异性散射图案位于观察到由于热振动而产生的散射。我们的定量分析表明，通过单缺陷近似的黄扩散散射（HDS）理论可以很好地描述所观察到的各向异性X射线扩散散射强度，这表明Sr掺杂物随机分布在晶体中。基于拟合参数，重构了Sr-掺杂剂诱导的弹性晶格畸变模式。 Sr掺杂物附近弹性晶格畸变的大幅度表明，Sr掺杂物引起的局部结构调制可能是通过扫描隧道显微镜实验观察到的电子不均匀性的起源。YBa2Cu3O6.92中的氧空位的行为不同。我们的X射线扩散散射测量结果表明，大多数氧空位都趋于聚集在一起，并有序地形成一个4单元细胞的上层结构，沿a *方向q＆ar; 0 =（¼，0，0）。超晶格分别由Cu，Ba和O原子的大各向异性位移组成，并且似乎与O阶“ Ortho-IV”相的存在一致。这些“ Ortho-IV”少数相岛也向周围的晶格诱发了远距离应变，这在我们的实验中表现为HDS。我们的定量分析进一步揭示了岛内的b方向晶格调制，其波矢为q＆ar; 1 =（0，0.21，0）。 q＆ar; 1非常接近连接源自金属Cu-O链的几乎嵌套的费米表面（FS）“脊”的嵌套向量，这一事实强烈表明b方向调制是由FS效应引起的。

著录项

  • 作者

    Liu, Xuerong.;

  • 作者单位

    University of California, San Diego.;

  • 授予单位 University of California, San Diego.;
  • 学科 Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 148 p.
  • 总页数 148
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 O49;
  • 关键词

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