Neutron Scattering Studies of Solids with Strong Fluctuations

强波动固体的中子散射研究

• 批准号: 0074571
• 负责人: Collin Broholm
• 金额: $ 33万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-05-15 至 2003-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0074571&HistoricalAwards=false
• 关键词: Neutron; Scattering; Studies; Solids; Strong

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.

该项目探索固体的动力学性质，其磁性，电子或结构性质的强烈波动。自旋系统中的杂质束缚态将通过磁中子散射进行研究。这些实验使用杂质来揭示宿主中的局部动态相关性，也将促进我们对强烈波动系统中杂质的了解。横向晶格振动可以使固体随着温度的升高而收缩。负热膨胀材料的晶格动力学将通过非弹性中子散射来研究。磁体中的受抑相互作用可以抑制有序性，并产生具有强局部约束的波动相位。中子散射将用于建立晶体模型系统中的自旋哈密顿量，并提供有关动力学相关性的详细信息。将进行实验以检查金属中的强磁波动。实验将探讨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，并探讨几何阻挫在这些系统中的作用。该项目的教育目标是创造中子散射技术的意识，并产生创新和有能力的实验物理学家，可以在未来十年内为国家最大的科学项目做出贡献并利用该项目：中子源。虽然固体在宏观尺度上表现为静态，但它们在纳米尺度上是动态的。理解这种运动是很重要的，特别是当技术推动更小的尺寸。本计画利用非弹性中子散射，探讨奈米长度尺度与皮科时间尺度的固体涨落。重点是在波动发挥重要作用的材料在某些材料与磁性原子，量子波动完全抑制任何宏观磁响应。然而，杂质可以在这些系统中引起磁性，就像杂质增加半导体的电导率一样。将进行实验以了解这些系统中接近杂质的磁性。大多数固体受热时会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，以确定什么类型的原子运动导致收缩竞争的相互作用可能导致磁铁的强烈波动。人们对这些起伏的磁体了解甚少，将通过磁中子散射进行检查。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，培养出能够为未来十年国家最大的科学项目做出贡献并从中受益的创新和有能力的科学家。中子源。