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Analysis of the gap in high-temperature superconductors using photoemission spectroscopy.

机译：用光发射光谱分析高温超导体中的间隙。

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摘要

The discovery of the cuprate superconductors has led to intensive research activity aimed at discovering the mechanism of high temperature superconductivity. A key feature in the electronic structure of a superconductor is the energy gap in the excitation spectrum. While gaps have been detected in the cuprate superconductors, traditional techniques for measuring the gap often give confusing or inconsistent results. The high transition temperatures and correspondingly large gaps of the cuprate superconductors have allowed photoemission spectroscopy to be used for the first time as a technique for studying the superconducting gap. Advantages of photoemission include that it is a direct measure of the gap, the surface studied is by necessity a clean, well defined region with variable depth, and the gap can be measured as a function of position in k-space. The largest disadvantage of photoemission as a tool for studying the gap is that the best resolution available so far is only on the order of the gap size. This makes a determination of gap size difficult. We have used photoemission to study the behavior of the gap near the surface of Bi{dollar}sb2{dollar}Sr{dollar}sb2{dollar}CaCu{dollar}sb2{dollar}O{dollar}sb{lcub}8+delta{rcub}{dollar} and its variation as a function of k position. We have found that the gap does not diminish near the surface, an indication of the highly two dimensional nature of these materials. Our photoemission experiment has shown no evidence of a proximity effect in a metal overlayer. We have also found that the gap is anisotropic in k space within the planes themselves. In particular, by measuring how the gap varies with k, we can gain information on the symmetry of the gap function. Our data is consistent with a mixed s+id symmetry gap and possibly with a pure d wave gap. Determining the symmetry of the gap provides one of the most stringent experimental constraints on the theory of high T{dollar}sb{lcub}rm c{rcub}{dollar} superconductivity yet found. We compare our result with other experiments which measure the gap in order to attempt to provide a complete and consistent picture of what is presently known of the behavior of the superconducting gap in cuprate superconductors.
机译：铜酸盐超导体的发现导致了旨在发现高温超导机理的深入研究活动。超导体电子结构的关键特征是激发光谱中的能隙。尽管已在铜酸盐超导体中检测到间隙，但传统的间隙测量技术通常会产生混乱或不一致的结果。铜酸盐超导体的高转变温度和相应的大间隙使得光发射光谱法首次被用作研究超导间隙的技术。光发射的优点包括它是间隙的直接量度，所研究的表面必然是一个干净的，界限分明的，深度可变的区域，并且可以根据k空间中的位置来测量间隙。作为研究间隙的工具，光发射的最大缺点是，迄今为止可获得的最佳分辨率仅在间隙尺寸的数量级上。这使得难以确定间隙尺寸。我们已经使用光发射来研究Bi {dollar} sb2 {dollar} Sr {dollar} sb2 {dollar} CaCu {dollar} sb2 {dollar} O {dollar} sb {lcub} 8 + delta表面附近的间隙行为{rcub} {dollar}及其随k位置的变化。我们发现，间隙在表面附近并没有减小，这表明这些材料具有很高的二维性质。我们的光发射实验表明，没有证据表明金属覆盖层具有邻近效应。我们还发现，间隙在平面本身内的k空间中是各向异性的。特别地，通过测量间隙如何随k变化，我们可以获得有关间隙函数对称性的信息。我们的数据与混合的s + id对称间隙以及可能的纯d波间隙一致。确定间隙的对称性是目前尚未发现的高T超导理论中最严格的实验约束之一。我们将我们的结果与测量间隙的其他实验进行比较，以试图提供关于铜酸盐超导体中超导间隙行为的最新信息的完整一致的图像。

著录项

  • 作者

    Wells, Barrett Otis.;

  • 作者单位

    Stanford University.;

  • 授予单位 Stanford University.;
  • 学科 Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 1992
  • 页码 144 p.
  • 总页数 144
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 O49;
  • 关键词

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