Studies of Solid 4-Helium

固体 4-氦的研究

• 批准号: 0855954
• 负责人: Robert Hallock
• 金额: $ 26万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-15 至 2014-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0855954&HistoricalAwards=false
• 关键词: Studies; Solid; Helium

****NON-TECHNICAL ABSTRACT****This research project is centered on an investigation of a fundamental and important current question in Condensed Matter Physics: Is it possible (and if so, what is the mechanism) for 4He atoms to flow though solid 4He. Prior work by others has suggested that this strange phenomenon might be possible and that there may be a ?supersolid? state of matter that may exist in solid 4He at very low temperatures. A ?supersolid? would represent a new quantum state of matter, therefore the question of its existence has aroused intense interest in the Condensed Matter community, stimulated a number of experiments and theoretical works, and resulted in a number of possible explanations and some substantial paradoxes. To determine whether it is possible for 4He atoms to flow through solid 4He, this project will impose a pressure difference across the solid by a unique technique that does not employ pushing on the crystal sides of the solid. Instead, application of a pressure difference is made to liquid helium that interfaces the solid on its sides. The approach employs the known behavior of 4He to remain a liquid at elevated pressure in Vycor (a porous glass). The pressure is applied to the liquid helium in the Vycor and atoms are fed into the solid helium through the interface where the Vycor meets the solid. The students involved in these studies will gain experience in fundamental physics and cutting-edge technology. They will work toward a Ph.D. degree and at graduation will be poised to contribute to scientific research and technological development in industrial, national laboratory, and academic settings.****TECHNICAL ABSTRACT****This research project is centered on an investigation of a fundamental and important current question in Condensed Matter Physics: Is it possible for 4He atoms to flow though solid 4He and if so, what is the mechanism. Prior work by others has suggested such flow might be possible and more specifically that there may be a ?supersolid? state of matter that may exist in solid 4He at very low temperatures. A ?supersolid? would represent a new quantum state of matter, therefore the question of its existence has aroused intense interest in the Condensed Matter community, stimulated a number of experiments and theoretical debate, and resulted in a number of possible explanations and some substantial paradoxes. The theoretical debate insists that perfect crystals of solid helium cannot be a ?supersolid?, and that any mass flux through the solid must be carried by defects. Various defect mechanisms have been proposed. To investigate the possibility of mass flux through solid 4He, this project will impose a chemical potential gradient on the solid by a unique technique: application of a pressure difference to liquid helium that interfaces the solid instead of applying pressure directly to the 4He crystal lattice. This approach employs the known behavior of 4He to remain a liquid at elevated pressure in Vycor (a porous glass), at pressures at which bulk 4He would be a solid. Application of a chemical potential difference across solid helium flanked by Vycor will allow atoms to be injected into the solid without application of a mechanical pressure difference to the lattice. Studies as a function of temperature and pressure will provide evidence (or not) for flow and limit the set of possible mechanisms that are responsible for flow. The students involved in these studies will gain experience in fundamental physics and cutting-edge technology. Upon completion of Ph.D. dissertations they will be poised to contribute to scientific research and development in industrial, national laboratory, and academic settings.

* 非技术摘要 * 本研究项目的核心是对凝聚态物理学中一个基本而重要的当前问题的研究：4He原子是否可能流过固体4He（如果可能，机制是什么）。其他人先前的工作表明，这种奇怪的现象可能是可能的，可能有一个？超固体？在非常低的温度下可能存在于固体4He中的物质状态。 一个？超固体？它代表了一种新的物质量子态，因此它的存在问题引起了凝聚态学界的强烈兴趣，激发了许多实验和理论工作，并导致了许多可能的解释和一些实质性的悖论。 为了确定4He原子是否有可能流过固体4He，该项目将通过一种独特的技术在固体上施加压力差，该技术不需要推动固体的晶体侧。相反，压力差的应用是对液氦进行的，液氦在其侧面与固体交界。该方法采用了已知的行为4He保持在Vycor（多孔玻璃）中的高压液体。压力施加到Vycor中的液氦上，原子通过Vycor与固体接触的界面进入固体氦。参与这些研究的学生将获得基础物理和尖端技术的经验。他们将攻读博士学位。学位和毕业将准备在工业，国家实验室和学术环境中为科学研究和技术发展做出贡献。技术摘要 * 本研究项目的核心是对凝聚态物理学中一个基本而重要的当前问题的研究：4He原子是否可能流过固体4He，如果可能，其机制是什么。其他人先前的工作表明，这种流动可能是可能的，更具体地说，可能有一个？超固体？在非常低的温度下可能存在于固体4He中的物质状态。一个？超固体？它代表了一种新的物质量子态，因此它的存在问题引起了凝聚态学界的强烈兴趣，激发了许多实验和理论争论，并导致了许多可能的解释和一些实质性的悖论。理论上的争论坚持认为，固体氦的完美晶体不可能是一个？超固体？并且通过固体的任何质量通量必须由缺陷携带。已经提出了各种缺陷机制。为了研究通过固体4He的质量通量的可能性，该项目将通过一种独特的技术在固体上施加化学势梯度：将压力差施加到固体界面的液氦上，而不是直接向4He晶格施加压力。这种方法利用了4He的已知行为，在Vycor（多孔玻璃）中在高压下保持液体，在这种压力下，大块4He将是固体。 在两侧为Vycor的固体氦上施加化学势差将允许原子注入固体中，而无需对晶格施加机械压力差。作为温度和压力函数的研究将提供流动的证据（或不提供），并限制负责流动的可能机制。参与这些研究的学生将获得基础物理和尖端技术的经验。完成博士学位后他们将准备在工业，国家实验室和学术环境中为科学研究和发展做出贡献。