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铜超导体“母化合物”铜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，残余反铁磁性知之甚少。该实验项目将通过使用可见光、紫外线或x射线光子的散射实验来澄清残余反铁磁性，以研究电子从占据的初始状态过渡到未占据的最终状态的激发，并伴随着电荷的重新分配。目标是(1)了解电子电荷激发如何与电子自旋激发（磁振子）耦合，并降低能量的电子电荷激发，其中可能包括超导间隙激发；(2)验证非弹性x射线散射技术在有限动量转移下研究电子电荷激发；(3)利用非弹性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。实验将采用低能和高能光子探针的组合。这些包括低能光吸收；共振拉曼散射，特别是共振双磁振子散射；紫外激发拉曼散射，以及两种新技术，非弹性s射线散射光谱（IXSS）和共振非弹性x射线散射光谱（RIXSS），提供有限动量传递的数据。这项工作有望推进强相关电子系统和非弹性x射线散射的知识。这个研究项目通过实验研究“掺杂”成为高温超导体的铜化合物的不寻常行为。这些“母体化合物”表现出不寻常的行为，包括反铁磁性，在某种程度上保留在超导相中。我们认为，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异常强的超导性是必要的。目前的实验项目将通过对这些化合物的光子散射（可见光、紫外线和x射线）的测量组合来解决有关反铁磁行为的重要问题。这项工作的一部分将利用拉曼效应，另一部分将利用一种新的先进实验技术，即非弹性x射线散射，这种技术现在可以在位于阿贡国家实验室附近的世界级同步加速器先进光子源上使用。这项工作将推进强相关电子系统和非弹性x射线散射过程的知识。对这些材料及其不寻常的磁性的研究是有价值的，可以作为铜酸盐的磁性、光学和电学性质理论的试验场，然后可以更有信心地应用于其他系统；在寻找新特性和新化合物的过程中，它们可能会在技术上找到新的应用。该研究项目是跨学科的，涉及研究生和博士后，他们将接受良好的培训，进入工业，政府或教育岗位。＊＊＊

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. ***