Photoemission Investigation of Collective Excitations in Novel Materials

w：\awards\awards96\num.doc 9705210沈 这 实验 项目是 基于 对 角度 分辨光电子能谱在表征 新材料的集体激发。实验的目标是提供关键的实验数据，以刺激发展的一个模拟的Nambu-Eliashberg理论的动量分辨光谱功能的系统中，准粒子激发强烈耦合到集体激发，如声子或自旋波动。感兴趣的材料是有机导体和超导体，掺杂的C60，A15化合物，BiK BiO 3和高Tc超导体。同步加速器辐射和紫外激光器将被用作激发源。 本实验研究项目使用角分辨光电子能谱技术测量当前科学和技术感兴趣的材料的晶体样品中特征激发的能量和晶体动量。 在这项技术中，具有特定方向（动量）和能量（波长）的光子落在感兴趣的材料的干净表面上。光电效应导致电子从材料的表面层发射。 这些光电子的检测方式是同时测量它们的数量、方向和动能。 这些数据，利用能量和动量守恒的原则，使详细的信息，以获得集体激发的样品。在这项工作中，感兴趣的材料包括几种不同的不寻常的电子导体，包括电子导电（碱金属）薄膜， 掺杂）碳六十，和一些不寻常的 类型 超导体，包括立方铋钾氧化钡和高Tc铜酸盐。这项工作的目的是提供优秀的数据，使理论家能够提出和测试这些系统中电子与“集体模式”（包括晶格振动（声子）和自旋波）相互作用的详细模型。 人们希望，对于这些更复杂的材料，也可以找到一种类似于成功的Nambu-Eliashberg理论的理论，用于传统超导体（如铅和汞）中的电子和声子， 应用程序. 这 研究 项目 是跨学科的性质，涉及研究生谁将得到良好的培训，进入工业，政府或教育职位。 ***

w:\awards\awards96\num.doc 9705210 Shen This experimental project is based on angle resolved photoemission spectroscopy in characterizing the collective excitations of novel materials. The goal of the experiments is to provide critical experimental data to stimulate the development of an analog of the Nambu-Eliashberg theory for momentum resolved spectral function in systems where the quasiparticle excitation is strongly coupled to collective excitations such as phonons or spin fluctuations. Materials of interest are organic conductors and superconductors, doped C60, A15 compounds, BiK BiO3, and high Tc superconductors. Synchrotron radiation and a UV laser will be used as the excitation source. %%% This experimental research project uses the technique of angle resolved photoemission spectroscopy to measure the energy and crystal momentum of characteristic excitations in crystalline specimens of materials of current scientific and technological interest. In this techniq light photons of well specified direction (momentum) and energy (wavelength) fall upon a clean surface of the material of interest. The photoelectric effect leads to emission of electrons from the surface layers of the material. These photoelectrons are detected in such a way that their number, direction and kinetic energy are simultaneously measured. These data, making use of principles of energy and momentum conservation, allow detailed information to be obtained on the collective excitations of the sample. In this work the materials of interest include several different unusual electonic conductor, including films of electronically conducting (alkali- metal doped) carbon-sixty, and several unusual types of superconductors, including a cubic Bismuth Potassium Barium Oxide and high Tc cuprates. The intent of the work is to provide excellent data which may permit theorists to propose and test detailed models for the interaction of electrons in these systems with "collective modes" including lattice vibrations (phonons) and spin waves. It is hoped that a theory analogous to the successful Nambu-Eliashberg theory for electrons and phonons in conventional superconductors such as lead and mercury, might also be found for these more complicated materials of possible technological application. This research project is interdisciplinary in nature and involves graduate students who will be excellently trained to enter positions in industry, government or education. ***