Study of Excitations in Cuprate Superconductors and Related Systems by Inelastic Scattering of Visible, Ultraviolet, and X-Ray Photons

这个实验研究项目的重点是作为铜酸盐超导体“母体化合物”的那些铜酸盐化合物的不同寻常的电子性质。这些化合物表现出相关的电子行为，特别是反铁磁性。在超导相中，人们对剩余反铁磁性知之甚少。这个实验项目将通过使用可见光、紫外光或x射线光子的散射实验来阐明剩余的反铁磁性，以研究电子从被占据的初始态转变到未被占据的终态的激发，并伴随着电荷的重新分配。其目的是(1)了解电子电荷激发如何与电子自旋激发(磁子)耦合并降低电子电荷激发的能量，其中可能包括超导能隙激发；(2)验证用于研究有限动量转移电子电荷激发的非弹性x射线散射技术；(3)通过使用非弹性x射线散射技术更好地理解传统金属和半导体中的电子激发。这些实验将使用低能和高能光子探测器的组合。其中包括低能光吸收；共振拉曼散射，特别是共振双磁振子散射；紫外拉曼散射；以及两种新技术，非弹性S散射光谱和共振非弹性X射线散射光谱，它们提供了有限动量转移的数据。预计这项工作将促进对强关联电子系统和非弹性x射线散射的了解。这个研究项目从实验上研究了铜酸盐化合物的反常行为，这些化合物在“溶解”后会变成高温超导体。这些“母化合物”表现出不同寻常的行为，包括反铁磁性，这在某种程度上保留在超导相中。人们认为，更好地了解这些材料的正常相和母相，对于理解适当掺杂时的异常强大的超导电性是必要的。目前的实验项目将通过测量这些化合物对光子(可见光、紫外光和X射线)的散射来解决有关反铁磁性行为的重要问题。一部分工作将利用拉曼效应，另一部分将利用一种新的先进实验技术--非弹性x射线散射，该技术现已在先进光子源上获得，先进光子源是一种世界级的同步辐射光源，位于阿贡国家实验室附近。这项工作将促进对强关联电子系统和非弹性x射线散射过程的了解。对这些材料及其特殊磁性的研究是铜酸盐磁性、光学和电学性质理论的试验场，然后可以更自信地应用于其他系统，并在寻找可能在技术上找到新应用的新性质和新化合物方面具有价值。这项研究项目本质上是跨学科的，涉及研究生和博士后，他们将接受良好的培训，以进入工业、政府或教育职位。***

w:\awards\awards96\num.doc 9705131 Klein This experimental research project focuses on the unusual electronic properties of those cuprate compounds which are "parent compounds" of the cuprate superconductors. These compounds exhibit correlated electron behavior, and in particular antiferromagnetism. In the superconducting phases, the residual antiferromagnetism is poorly understood. This experimental project will clarify the residual antiferromagnetism by scattering experiments using visible, ultraviolet, or x-ray photons, to study excitations wherein an electron from an occupied initial state makes a transition to an unoccupied final state, accompanied by a redistribution of charge. The objectives are (1) to understand how electronic charge excitations couple to electronic spin excitations (magnons) and to lower energy electronic charge excitations, which may include superconducting gap excitations; (2) to validate inelastic x-ray scattering techniques for studying electronic charge excitations at finite momentum transfer; (3) to better understand electronic excitations in conventional metals and semiconductors through use of inelastic x-ray scattering techniques. The experiments will employ a combination of low energy and high energy photon probes. These include low energy optical absorption; resonance Raman scattering, especially resonant two-magnon scattering; UV excited Raman scattering, and two new techniques, inelastic s-ray scattering spectroscopy (IXSS) and resonant inelastic x-ray scattering spectroscopy (RIXSS), which provide data at finite momentum transfer. The work is expected to advance knowledge of both strongly-correlated electronic systems and of inelastic x- ray scattering. %%% This research project experimentally studies the unusual behavior of the cuprate compounds which when "dop ed" become high temperature superconductors. These "parent compounds" exhibit unusual behavior, including antiferromagnetism, which is to some extent retained in the superconducting phases. It is believed that a better understanding of the normal and parent phases of these materials is necessary for understanding of the unusually strong superconductivity when suitably doped. The present experimental project will address the important questions concerning the antiferromagnetic behavior, by a combination of measurements of the scattering of photons (visible, ultraviolet, and x-ray) by these compounds. A portion of the work will utilize the Raman effect, and another portion will utilize a new advanced experimental technique, inelastic x-ray scattering, which is now available at the Advanced Photon Source, a world-class synchrotron light source which is located near the Argonne National Laboratory. The work will advance knowledge of both strongly-correlated electronic systems and also of the inelastic x-ray scattering process. The study of these materials and their unusual magnetism is valuable as a testing ground for theories of magnetic, optical, and electrical properties of the cuprates, which can then be more confidently applied to other systems; and in the search for novel properties and new compounds which may find new application in technology. This research project is interdisciplinary in nature and involves both graduate and postdoctoral students who will be excellently trained to enter positions in industry, government or education. ***