Collaborative Research: Synchrotron X-Ray Scattering Experiments on Solid Helium

合作研究：固体氦同步加速器X射线散射实验

• 批准号: 0804554
• 负责人: Moses Chan
• 金额: $ 5.1万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-09-15 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0804554&HistoricalAwards=false
• 关键词: Collaborative; Research; Synchrotron; Ray; Scattering

****NON-TECHNICAL ABSTRACT****This collaborative award supports a program primarily directed towards issues that stem from recent experimental observations of a supersolid state. A supersolid is a new state of matter in which part of the atoms in the solid show frictionless motion with respect to the rest of the solid, or the container that holds it. This resembles such phenomena as superconductivity and superfluidity. The precise nature of the supersolid state is currently a matter of lively debate. A combination of mechanical and x-ray experiments aims at correlating phenomena observed at the macroscopic level with the microscopic structure of the solid. This will provide critical information for a more general understanding of supersolidity. The project is a vehicle for intensive and sustained collaboration between research groups at the University of Delaware, Western Michigan University, Northern Illinois University, and Pennsylvania State University focused on experiments at the Advanced Photon Source at Argonne National Laboratory. This setting gives both the undergraduate and graduate students involved a much wider view of the physics enterprise, and their potential role in it, than is usually the case. It also provides a mechanism for the students to build up a network of contacts among peers early on and forms an excellent preparation for a scientific career.****TECHNICAL ABSTRACT****The central goal of this collaborative project is to provide critical information necessary to interpret recent observations of a possible supersolid state in 4He. A series of combined x-ray diffraction, torsional oscillator (TO) and dielectric constant experiments will be used to investigate several questions: 1. Are there features in the x-ray diffraction directly indicative of a supersolid transition? E.g., a careful study of the Debye-Waller factor may provide limits on the Bose condensate fraction. 2. What aspects of crystal quality are important for the formation of a supersolid state? X-ray measurements will be used to determine the crystal quality, and will be combined with TO measurements in a simultaneous experiment. In addition, disorder will be introduced in a controlled way by growing the solid in porous media such as aerogels. 3. Does 4He form a commensurate solid at T = 0, or is the zero-point vacancy concentration 0? High precision measurements of the temperature dependence of the lattice constants at constant volume, can distinguish between thermal and non-thermal vacancy populations. The training of graduate as well as undergraduate students forms an important part of this project. Its collaborative nature, as well as the fact that part of the work is done at the APS/ANL, gives students a much broader exposure to modes of research than is normally the case, and will form an excellent preparation for a scientific career.

****非技术摘要****该合作奖项支持一个主要针对最近超固态实验观察所产生问题的项目。超固体是一种新的物质状态，其中固体中的部分原子相对于固体的其余部分或容纳固体的容器表现出无摩擦运动。这类似于超导性和超流动性等现象。超固态的确切性质目前是一个激烈争论的问题。机械和 X 射线实验的结合旨在将宏观层面观察到的现象与固体的微观结构联系起来。这将为更普遍地理解超固体提供关键信息。该项目是特拉华大学、西密歇根大学、北伊利诺伊大学和宾夕法尼亚州立大学研究小组之间深入和持续合作的工具，重点关注阿贡国家实验室先进光子源的实验。与通常的情况相比，这种设置使本科生和研究生对物理事业及其潜在角色有了更广泛的了解。它还为学生提供了一种尽早在同龄人之间建立联系网络的机制，并为科学职业生涯做好了良好的准备。****技术摘要****该合作项目的中心目标是提供关键的信息解释最近对 4He 中可能的超固态的观察结果所必需的信息。一系列组合的 X 射线衍射、扭转振荡器 (TO) 和介电常数实验将用于研究以下几个问题： 1. X 射线衍射中是否有直接指示超固体转变的特征？例如，仔细研究德拜-沃勒因子可能会限制玻色凝聚分数。 2. 晶体质量的哪些方面对于超固态的形成很重要？ X 射线测量将用于确定晶体质量，并将与 TO 测量相结合进行同步实验。此外，通过在气凝胶等多孔介质中生长固体，可以以受控方式引入无序。 3. 4He 在 T = 0 时是否形成相应的固体，或者零点空位浓度为 0？高精度测量恒定体积下晶格常数的温度依赖性，可以区分热空位和非热空位。研究生和本科生的培训是该项目的重要组成部分。它的协作性质，以及部分工作是在 APS/ANL 完成的事实，使学生能够比通常情况更广泛地接触研究模式，并将为科学职业生涯做好良好的准备。