Investigations of Solid Helium

固体氦的研究

• 批准号: 1205217
• 负责人: Robert Hallock
• 金额: $ 58万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-06-01 至 2017-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1205217&HistoricalAwards=false
• 关键词: Investigations; Solid; Helium

****Technical Abstract****This project is centered on an investigation of a fundamental and important current question in Condensed Matter Physics: What is the mechanism by which 4He atoms are apparently able to flow though solid 4He? Prior controversial work by others has suggested that there may be a "supersolid" state of matter that may exist in solid 4He at very low temperatures. This is an issue that 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. 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. Some believe that a previously unknown plasticity mechanism may be at work. The experimental approach used in this research is to impose a chemical potential gradient on the solid by a unique technique: for example, application of a pressure difference to liquid helium that interfaces the solid instead of applying pressure directly to the 4He crystal lattice; or, the application of a temperature difference to utilize the superfluid Fountain Effect. The 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. Studies as a function of temperature and pressure (and 3He impurity concentration) will provide further evidence for flow and limit the set of possible mechanisms that are responsible for flow. The students (undergraduate, graduate) and post-graduate (postdocs) involved in these studies will gain experience in fundamental physics and cutting-edge technology. Graduating students will be poised to contribute to scientific research and technological development in industrial, national laboratory, and academic settings.****Non-Technical Abstract****This research is centered on an investigation of a fundamental and important current question in Condensed Matter Physics: What is the mechanism by which 4He atoms are apparently able to flow though solid 4He? Prior controversial work by others has suggested that there may be a "supersolid" state of matter that may exist in solid 4He at very low temperatures. This is an issue that 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. Some believe that a previously unknown plasticity mechanism may be at work. Most agree that disorder in the solid is a crucial ingredient. The approach used in this research is to impose, for example, 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 superfluid liquid helium that interfaces the solid on its sides using the unique properties of superfluid helium in a porous material that contains the superfluid. Participating undergraduate, graduate and post-graduate (postdocs) students will gain experience in fundamental physics and cutting-edge technology. These investigations may lead to advances in materials science that could have significant technological implications, for example in metallurgy.

****技术摘要****该项目的重点是对凝结物理学中一个基本和重要的当前问题的调查：4He原子显然能够通过固体4HE流动的机制是什么？ 其他人的事先有争议的工作表明，在非常低的温度下，在4HE中可能存在“超olid”状态。 这个问题引起了人们对凝结物质社区的强烈兴趣，刺激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。 理论上的辩论坚持认为，固体氦气的完美晶体不能是“超胚膜”，并且必须通过缺陷来携带任何质量通量。 已经提出了各种缺陷机制。 有些人认为以前未知的可塑性机制可能正在起作用。 这项研究中使用的实验方法是通过一种独特的技术对固体施加化学势梯度：例如，将压力差施加到液态氦气中，该液氦将固体接口而不是直接向4HE晶体晶格施加压力；或者，使用温度差来利用超流源喷泉效应。该方法采用4HE的已知行为，以在Vycor（多孔玻璃）中保持液体，在压力下，散装4HE是固体的压力。 研究随温度和压力的函数（以及3HE杂质浓度）将为流动提供进一步的证据，并限制导致流量的可能机制。 参与这些研究的学生（本科生，研究生）和研究生（博士后）将获得基本物理和尖端技术的经验。即将毕业的学生将有助于为工业，国家实验室和学术环境中的科学研究和技术发展做出贡献。****非技术摘要****这项研究集中在调查凝结物质物理学中基本和重要问题的研究中：4he原子在哪些机制中可以表现出什么机制，尽管有什么能力流动4he solid 4he？ 其他人的事先有争议的工作表明，在非常低的温度下，在4HE中可能存在“超olid”状态。 这个问题引起了人们对凝结物质社区的强烈兴趣，刺激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。 有些人认为以前未知的可塑性机制可能正在起作用。 大多数人认为，固体中的疾病是至关重要的成分。 这项研究中使用的方法是通过一种独特的技术在固体之间施加压力差，该技术不会在固体的晶体侧推动。取而代之的是，将压力差的应用用于超流体液氦，该液态氦气在包含超氟的多孔材料中使用超氟氦的独特特性接口其侧面的固体。参加的本科，研究生和研究生（博士后）学生将获得基本物理和尖端技术的经验。这些研究可能会导致材料科学的进步，这些技术可能具有重要的技术意义，例如冶金学。