Kinetics of Charge-Density Waves: Time-Resolved X-Ray Scattering Studies

w：\awards\awards96\*.doc 9801792 Brock 本实验研究计画系关于准一维材料之电荷密度波传导过程。具体而言，该项目研究了由诸如NbSe 3的材料中的随机分布的缺陷对CDW的钉扎。 这被认为是一个模型系统的一维金属，并指出，在许多情况下，数学描述的CDW的运动是相同的方程描述的材料的生长或在高Tc超导体的磁通线晶格的运动。因此，对CDW行为的新理解在这些其他背景下也可能是有用的。 实验项目的重点是CDW的动力学，以及这些动力学如何受到淬火随机缺陷的影响。 这种钉扎缺陷的影响，寻求平衡，近平衡和高度非平衡CDW系统的动力学。 所采用的实验探针是X射线衍射，使用由现代同步加速器源的高强度实现的最先进的方法。所采用的方法是时间分辨高分辨率衍射、微衍射、准弹性散射和非弹性散射。 这些技术的测量集中在CDW状态的相位波动的时间依赖性的淬火随机杂质的影响。这些数据将用于对当前的几种理论进行定量测试。 这个研究项目是跨学科的性质，涉及一个或多个博士后 和研究生， 优秀的培训，为工业，政府实验室或学术界的职业生涯做准备。 这个实验研究项目是关于一类被称为“准一维金属”的导电材料中发生的不寻常的导电过程。 这种材料是NbSe 3，其形成反映该材料的一维或线性趋势的针状晶体。在这些材料中，电子电荷只能在一个方向上移动，沿着针状晶体。 这与铜等普通金属的电子运动是三维的，以及石墨等物质的运动基本上被限制在一个平面上是完全不同的。 在一维情况下会出现特殊的效应，其中之一称为电荷密度波（CDW）。在这种情况下，当代表所有电子沿着晶体的相关运动的CDW波作为一个单元一起运动时，发生导电。这是关联电子运动的一个极端例子。 这 类型 准一维材料中导电过程的研究是本实验项目的重点。所采用的实验探针是X射线衍射，使用由现代同步加速器源的高强度实现的最先进的方法。所采用的方法是时间分辨高分辨率衍射，微衍射， 准弹性 散射 和 非弹性散射在这项研究中获得的信息将增加有关固态材料导电的知识基础，并可能导致新型电子器件。这个研究计划是跨学科的性质，涉及一个或多个博士后和研究生，谁收到 为职业生涯做准备的优秀培训 在工业界、政府实验室或学术界。 ***

w:\awards\awards96\*.doc 9801792 Brock This experimental research project is concerned with charge- density-wave (CDW) conduction processes, in quasi-one-dimensional materials. Specifically, this project investigates the pinning of the CDW by the randomly distributed defects in a material such as NbSe3. This is considered a model system for a one-dimensional metal, and it is pointed out that the mathematical description of motion of a CDW is in many cases identical to equations describing growth of materials or the motion of a flux-line lattice in a high Tc superconductor. Thus new understanding on CDW behavior may be useful in these other contexts also. The experimental project focuses on the kinetics of the CDW and how these kinetics are affected by quenched random defects. The effects of such pinning defects are sought on the kinetics of equilibrium, near-equilibrium, and highly non-equilibrium CDW systems. The experimental probe employed is x-ray diffraction, using state of the art methods which are enabled by the high intensities of modern synchrotron sources. The methods to be employed are time-resolved high-resolution diffraction, micro- diffraction, quasi-elastic scattering and inelastic scattering. Measurements with these techniques focus on the time-dependence of the phase fluctuations of the CDW state as affected by quenched random impurities. The data will be used to perform quantitative tests of several current theories. This research program is interdisciplinary in nature and involves one or more postdoctoral and graduate students, who receive excellent training in preparation for careers in industry, government laboratories or academia. %%% This experimental research project is concerned with unusual electrical conduction processes which occur in a class of conducting materials which are call ed "quasi one dimensional metals". Such a material is NbSe3 which forms needle-like crystals which reflect the one-dimensional or linear tendencies of this material. In these materials, electronic charge can move only in one direction, along the needle-like crystal. This is quite unlike common metals like copper in which electron motion is three-dimensional, and substances like graphite, in which motion is confined essentially to a plane. There are special effects which occur in the one dimensional case, and one of these is called a charge-density-wave (CDW). In this case electrical conduction occurs when the CDW wave, representing a correlated motion of all the electrons along the crystal, moves together as a unit. This is an extreme example of correlated electron motion. This type of conduction process, in quasi-one-dimensional materials, is of considerable interest, and is the focus of this experimental project. The experimental probe employed is x-ray diffraction, using state of the art methods which are enabled by the high intensities of modern synchrotron sources. The methods to be employed are time-resolved high-resolution diffraction, micro-diffraction, quasi-elastic scattering and inelastic scattering. The information gained in this investigation will add to the base of knowledge about conduction of electricity in solid state materials, and could lead to new types of electronic devices. This research program is interdisciplinary in nature and involves one or more postdoctoral and graduate students, who receive excellent training in preparation for careers in industry, government laboratories or academia. ***