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

本实验研究项目涉及准一维材料中的电荷密度波（CDW）传导过程。具体而言，本项目研究了在NbSe3等材料中随机分布的缺陷对CDW的固定。这被认为是一维金属的模型系统，并指出CDW运动的数学描述在许多情况下与描述材料生长或高Tc超导体中通量线晶格运动的方程相同。因此，对CDW行为的新理解也可能在这些其他情况下有用。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。这种钉住缺陷的影响是寻求平衡，近平衡和高度非平衡CDW系统的动力学。实验探针采用的是x射线衍射，使用由高强度的现代同步加速器源实现的最先进的方法。采用的方法有时间分辨高分辨衍射、微衍射、准弹性散射和非弹性散射。这些技术测量的重点是受淬火随机杂质影响的CDW态相位波动的时间依赖性。这些数据将用于对几种现有理论进行定量检验。该研究项目是跨学科的，涉及一名或多名博士后和研究生，他们接受了良好的培训，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发生在一类被称为“准一维金属”的导电材料中的不寻常的导电过程。这种材料是NbSe3，它形成针状晶体，反映了这种材料的一维或线性倾向。在这些材料中，电荷只能沿一个方向移动，即针状晶体。这与铜等普通金属不同，铜的电子运动是三维的，而石墨等物质的运动基本上局限在一个平面上。在一维情况下会出现一些特殊的效应，其中一种叫做电荷密度波（CDW）。在这种情况下，当CDW波（代表所有电子沿晶体的相关运动）作为一个单位一起移动时，就会发生导电。这是相关电子运动的一个极端例子。在准一维材料中，这种类型的传导过程引起了相当大的兴趣，也是本实验项目的重点。实验探针采用的是x射线衍射，使用由高强度的现代同步加速器源实现的最先进的方法。采用的方法有时间分辨高分辨衍射、微衍射、准弹性散射和非弹性散射。在这项调查中获得的信息将增加关于固态材料导电的知识基础，并可能导致新型电子设备。该研究项目是跨学科的，涉及一名或多名博士后和研究生，他们接受了良好的培训，为工业、政府实验室或学术界的职业生涯做准备。* * *

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. ***