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Infrared properties of three low-dimensional materials.

机译：三种低维材料的红外特性。

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摘要

This thesis includes far-infrared measurements of three new and very different materials, the spin-Peierls compound CuGeO3, the quasi-two-dimensional organic superconductor kappa-(ET)2Cu[N(CN)2]Br, and the high-temperature superconductor HgBa2Ca2Cu 3O8-delta. All three have reduced dimensionality and exhibit properties which are both of great interest to solid state physicists and ideal for study using far-infrared techniques.; CuGeO3 is the first inorganic spin-Peierls compound to be discovered. It has a simple structure, is easily doped with impurities, and can be grown in the form of very large single crystals. These properties make it far easier to study than its organic predecessors. Like other spin-Peierls compounds, CuGeO3 consists of chains of large tightly bound blocks that can move as units, in this case GeO4 tetrahedra, and the spin-Peierls distortion can be described in terms of a displacement of these units. This thesis discusses a newly discovered local libration of the GeO4 tetrahedra near impurity atoms in doped CuGeO3. This unusual mode is highly anharmonic and causes striking features in the far-infrared spectra.; The superconductor kappa-(ET)2Cu[N(CN)2]Br belongs to a family of organic superconductors that, like the much studied high-temperature superconductors, consist of metallic sheets that are relatively isolated from one another. Conduction within the sheets is coherent, but the nature of the transport between the sheets is poorly understood. In this thesis, the first ever interplane far-infrared spectra for this material are reported. No evidence of coherent transport is found down to the lowest frequencies suggesting that in this respect this family of organic superconductors is similar to the high-temperature superconductors. Many internal modes of the ET molecule are also identified in the spectra.; HgBa2Ca2Cu3O8-delta has the highest superconducting transition temperature ever measured, but single crystals large enough for infrared and far-infrared studies have only recently become available. This thesis presents in-plane infrared measurements on this material that show the presence of a pseudogap much like that seen in other high temperature superconductors except that it is considerably larger in size. In fact, its pseudogap is larger than those of the other materials by the same factor by which its transition temperature is higher. This suggests a possible relationship between pseudogap size and transition temperature which is discussed in light of other results in the literature.; All three of these materials are either quasi-one-dimensional or quasi-two-dimensional in nature and demonstrate both the diversity of the phenomena found in solid state systems and the utility of far-infrared spectroscopy in their study.
机译：本论文包括三种不同的新材料的远红外测量：自旋-Peierls化合物CuGeO3，准二维有机超导体kappa-（ET）2Cu [N（CN）2] Br和高温HgBa2Ca2Cu3O8-δ超导体。这三者均具有减小的尺寸并表现出特性，这既是固态物理学家非常感兴趣的，也是使用远红外技术进行研究的理想选择。 CuGeO3是第一个被发现的无机自旋Peierls化合物。它具有简单的结构，易于掺杂杂质，并且可以以非常大的单晶形式生长。这些特性使其比其有机的前身更容易研究。像其他自旋Peierls化合物一样，CuGeO3由大块紧密结合的链组成，这些链可以作为单位移动，在这种情况下为GeO4四面体，自旋Peierls变形可以用这些单位的位移来描述。本文讨论了新发现的GeO4四面体在掺杂CuGeO3中杂质原子附近的局部释放。这种不寻常的模式是高度非谐波的，并在远红外光谱中引起惊人的特征。超导体kappa-（ET）2Cu [N（CN）2] Br属于有机超导体家族，就像人们研究的高温超导体一样，它们由彼此相对隔离的金属薄板组成。薄片内部的传导是连贯的，但是人们对薄片之间的传输性质了解得很少。在这篇论文中，报道了这种材料的第一个面内远红外光谱。直到最低频率都没有发现相干传输的证据，这表明在这一方面，有机超导体家族与高温超导体相似。光谱中还可以识别出ET分子的许多内部模式。 HgBa2Ca2Cu3O8-δ具有有史以来最高的超导转变温度，但是直到最近才有足够大的单晶用于红外和远红外研究。本文提出了在这种材料上的平面红外测量结果，显示出伪间隙的存在与在其他高温超导体中所见的伪间隙非常相似，只是其尺寸相当大。实际上，其伪间隙比其他材料的伪间隙大，而其过渡温度更高。这表明伪间隙尺寸和转变温度之间可能存在关系，该关系已根据文献中的其他结果进行了讨论。所有这三种材料本质上都是准一维的或准二维的，并且证明了固态系统中发现的现象的多样性以及远红外光谱在其研究中的实用性。

著录项

  • 作者

    McGuire, Jeffrey Joseph.;

  • 作者单位

    McMaster University (Canada).;

  • 授予单位 McMaster University (Canada).;
  • 学科 Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 2001
  • 页码 129 p.
  • 总页数 129
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 O49;
  • 关键词

  • 入库时间 2022-08-17 11:47:23

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