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

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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. ***