Photoemission Investigation of Collective Excitations in Novel Materials

这个实验项目基于角度分辨光电子能谱来表征新材料的集体激发。这些实验的目的是提供关键的实验数据，以刺激在准粒子激发与集体激发(如声子或自旋涨落)强耦合的系统中，动量分辨谱函数的Nambu-Eliashberg理论的模拟发展。感兴趣的材料是有机导体和超导体，掺杂C60，A15化合物，BiK BiO_3和高T_c超导体。将使用同步辐射和紫外光激光器作为激发源。这个实验研究项目使用角度分辨光电子能谱技术来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。在这种技术中，具有明确方向(动量)和能量(波长)的光子落在感兴趣材料的清洁表面上。光电效应导致电子从材料的表层发射。探测这些光电子的方法是同时测量它们的数目、方向和动能。这些数据利用能量和动量守恒原理，可以获得有关样品集体激发的详细信息。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(碱金属掺杂)碳-60薄膜，以及几种不寻常类型的超导体，包括立方铋钾巴氧化物和高T_c铜酸盐。这项工作的目的是提供极好的数据，使理论家能够提出和测试这些系统中电子与包括晶格振动(声子)和自旋波在内的“集体模”相互作用的详细模型。人们希望，对于这些可能具有技术应用的更复杂的材料，也可以找到类似于成功的Nambu-Eliashberg超导体中电子和声子的Nambu-Eliashberg理论的理论。这项研究项目本质上是跨学科的，涉及将接受良好培训以进入工业、政府或教育职位的研究生。***

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. ***