Neutron Scattering Studies of Solids with Strong Fluctuations

本项目探索具有磁性、电子或结构性质强烈波动的固体的动力学性质。用磁中子散射法研究自旋系统中的杂质束缚态。实验使用杂质来揭示宿主体内的局部动态相关性，也将促进我们对强波动系统中杂质的理解。横向晶格振动会使固体随着温度的升高而收缩。负热膨胀材料中的晶格动力学将通过非弹性中子散射来研究。磁体中受挫的相互作用可以抑制有序并产生具有强局部约束的波动相。中子散射将用于建立晶体模型系统中的自旋哈密顿量，并提供有关动态相关性的详细信息。将进行实验以检查金属中的强磁波动。实验将探索反铁磁有序重费米子系统中自旋波到电子空穴对激发的交叉，并探讨几何挫折在这些系统中的作用。该项目的教育目标是提高对中子散射技术的认识，培养具有创新能力的实验物理学家，为国家未来十年最大的科学项目“散裂中子源”做出贡献。虽然固体在宏观长度尺度上是静态的，但在纳米尺度上却是动态的。理解这种运动是很重要的，尤其是当技术向更小的维度推进时。本项目利用非弹性中子散射研究固体在纳米长度尺度和皮秒时间尺度上的波动。在某些具有磁性原子的材料中，量子涨落完全抑制了任何宏观磁响应。然而，杂质会在这些系统中产生磁性，就像杂质会增加半导体的导电性一样。将进行实验以了解这些系统中靠近杂质的磁性。大多数固体在受热时随着原子运动幅度的增大而膨胀。然而，在某些材料中，原子运动导致收缩。将进行实验以确定哪种类型的原子运动导致收缩，相互竞争的相互作用可导致磁体的强烈波动。人们对这些波动的磁体知之甚少，将通过磁中子散射进行研究。最后将进行实验来探测金属中导致异常金属性质和超导性的磁波动。该项目的教育目标是提高人们对中子散射技术的认识，培养具有创新能力的科学家，为未来十年国家最大的科学项目做出贡献。散裂中子源。

This project explores dynamical properties of solids with strong fluctuations of their magnetic, electronic or structural properties. Impurity bound states in spin systems will be examined through magnetic neutron scattering. The experiments use impurities to reveal local dynamic correlations in the host and will also advance our understand of impurities in strongly fluctuating systems. Transverse lattice vibrations can cause solids to contract with increasing temperature. Lattice dynamics in materials with negative thermal expansion will be examined through inelastic neu-tron scattering. Frustrated interactions in magnets can suppress ordering and give rise to fluctuating phases with strong local constraints. Neutron scattering will be used to establish the spin Hamiltonian in crystalline model systems and provide detailed information about dynamic correlations. Experiments will be performed to examine strong magnetic fluctuations in metals. The experiments will probe the crossover from spin wave to electron hole pair excitations in anti-ferromagnetically ordered heavy fermion systems and explore the role of geometrical frustration in these systems. The educational goal of the project is to create awareness of the neutron scattering technique and produce innovative and competent experimentalists physicists that can contribute to and take advantage of the nations largest scientific project in the next decade: The Spallation Neutron Source.%%%While solids appear static on macroscopic length scales, they are dynamic on the nanometer scale. Understanding such motion is important, especially as technology pushes to smaller dimensions. This project examines fluctuations in solids on the nanometer length scale and pico second time scale using inelastic neutron scattering. The focus is on materials where fluctuations play an important role In certain materials with magnetic atoms, quan-tum fluctuations completely suppress any macroscopic magnetic response. Impurities can however induce magnetism in these systems just as impurities increase the electric conduc-tivity of semiconductors. Experiments will be carried out to understand magnetism close to impurities in these systems. Most solids expand on heating as the amplitude of atomic motion increases. However in some materials, atomic motion leads to contracti6n. Experiments will be carried out to determine what type of atomic motion leads to contraction Competing interactions can lead to strong fluctuations in magnets. These fluctuating magnets are poorly understood and will be examined through magnetic neutron scattering. Finally experiments will be carried out to probe magnetic fluctuations in metals that lead to anomalous metallic properties and superconductivity. The educational goal of the project is to create awareness about the neutron scattering technique and produce innovative and competent scientists that can contribute to and take advantage of the nations largest scientific project in the next decade. The Spallation Neutron Source.