Fermi Surface Cross-Sectional Images from Photoelectron Angular Distributions

最近对薄膜磁性和高温超导等领域的兴趣强调了对费米表面进行详细测量的必要性。这个建议通过使用一种新开发的技术来解决这个问题，利用光电子能谱来确定费米表面。该技术通常适用于广泛的材料，并将提供关于体和表面系统的信息。它对低对称性区域的费米表面结构很敏感，并且可以在高温下进行研究，其中相变可能很重要。测量将使用一种新型的显示型电子能量分析仪进行，该分析仪将产生能量分辨的光电强度与发射角度的二维图像。这项工作将在路易斯安那州立大学高级微结构和器件中心（CAMD）同步加速器光源进行。最初的研究将涉及从以前的研究中得到充分理解的贵金属，随后将扩展到具有大量嵌套费米表面的金属。这些材料中的一些经历磁相变，其中费米表面的拓扑结构可以发生实质性变化；这样的实验将支持进一步的理论进展。这些技术也将应用于高温超导体，在那里将研究拦截费米表面的带的性质。由于该方法对k空间的大区域进行了采样，因此将对这些材料进行意想不到的特征调查，并将提供电子结构的快速概述。在适当的情况下，将使用常规仪器进行高分辨率研究。这项工作将与劳伦斯利弗莫尔实验室（Lawrence Livermore Laboratory）、其他大学的国家标准与技术研究所（National Institute of Standards and Technology）的研究人员合作完成。随着新型材料的开发，表征其相关性能的技术必须得到改进。这种需要将在一种新的显示型电子能量分析仪的开发中得到解决，以在成像模式下执行光电子能谱。测量依靠同步辐射从感兴趣的材料表面喷射电子；这种辐射将由LSU高级微结构和器件中心（CAMD）存储环提供。通过对发射方向的成像，可以探索材料费米表面的详细性质。这为材料行为的理论理解提供了有价值的信息，并为材料加工的改进提供了反馈。最初，该方法将应用于其他技术已经很好理解的金属系统。该方法将被改进，用于研究具有更复杂费米表面的材料，这些材料可以通过强迫它们经历磁相变来改变，并将用于展示该方法的灵活性。最后，由于铜氧化物中超导性的起源仍然难以捉摸，这种先进的仪器将应用于高温超导体。该项目为表征费米表面的电子态提供了一种新方法，并将提高对基本电子性质的理解。由于测量依赖于最高质量的材料，因此将与劳伦斯利弗莫尔实验室、国家标准研究所和其他大学的研究人员合作。//

Recent interest in areas such as thin-film magnetics and high temperature superconductivity have underscored the need for detailed measurements of Fermi surfaces. This proposal addresses the problem by using a newly developed technique using photoelectron spectroscopy to determine Fermi surfaces. The technique is generally applicable to a wide range of materials and will provide information on both bulk and surface systems. It is sensitive to the structure of the Fermi surface in regions of low symmetry and studies can be performed at elevated temperatures where phase transitions may be important. Measurements will be made using a novel display-type electron energy analyzer that will produce energy resolved two dimensional images of photoemission intensity versus emission angle. The work will be conducted at the LSU Center for Advanced Microstructure and Devices (CAMD) synchrotron light source. The initial investigations will involve noble metals which are well-understood from previous studies and will later be extended to metals with heavily nested Fermi surfaces. Some of these materials undergo magnetic phase transitions where the topology of the Fermi surface can change substantially; such experiments will support further theoretical progress. These techniques will also be applied to high temperature superconductors where the nature of the bands intercepting the Fermi surface will be investigated. Since the method samples large regions of k-space, these materials will be surveyed for unexpected features and will provide the rapid overviews of electronic structure. Conventional instrumentation will be used for high- resolution studies when appropriate. The work will be done in collaboration with researchers at Lawrence Livermore Laboratory, the National Institute of Standards and Technology at other universities. %%% As new classes of materials are developed, techniques for characterizing their relevant properties must improve. This need will be addressed in the development of a new display-type electron energy analyzer, to perform photoelectron spectroscopy in an imaging mode. The measurements rely on synchrotron radiation to eject electrons from surfaces of the material of interest; this radiation will be provided by the LSU Center for Advanced Microstructure and Devices (CAMD) storage ring. By imaging the directions of the emission, the detailed nature of the material's Fermi surface can be explored. This provides information that is valuable for a theoretical understanding of material behavior and gives feedback for improvements in materials processing. Initially, the method will be applied to metallic systems that are well understood by other techniques. The approach will refined to study materials with more complicated Fermi surfaces that can be altered by coercing them to undergo magnetic phase transitions and will be used to demonstrate the flexibility of the methodology. Finally, this advanced instrumentation will be applied to high temperature superconductors as the origin of superconductivity in the cuprate oxides remains elusive. The project provides a new method for characterizing the electronic states at the Fermi surface and will result in an improved understanding of fundamental electronic properties. As the measurements rely on the highest quality materials, collaboration with researchers at the Lawrence Livermore Laboratory, the National Institute of Standards, and at other universities will be undertaken.//