Studies of Solid 4-Helium

*非技术摘要*本研究项目是对凝聚态物理中一个基本而重要的当前问题的研究：4He原子是否可能(如果可能，其机制是什么)通过固体4He。其他人之前的工作已经表明，这种奇怪的现象可能是可能的，可能存在一种超固体？在很低的温度下可能存在于固体4He中的物质状态。A？超级固体？将代表物质的一种新的量子态，因此它的存在问题引起了凝聚态社区的强烈兴趣，刺激了许多实验和理论工作，并导致了一些可能的解释和一些实质性的悖论。为了确定4He原子是否可能通过固体4He流动，该项目将通过一种独特的技术在固体上施加压差，该技术不使用对固体晶体一侧的推动。取而代之的是，对液氦施加压差，液氦与其侧面的固体接触。该方法利用4He的已知行为，在Vycor(一种多孔玻璃)中保持高压下的液体。压力施加到Vycor中的液氦上，原子通过Vycor与固体相遇的界面进入固体氦中。参与这些研究的学生将获得基础物理和尖端技术方面的经验。他们将攻读博士学位，毕业后将为工业、国家实验室和学术机构的科学研究和技术发展做出贡献。*技术摘要*本研究项目的中心是对凝聚态物理中一个基本和重要的当前问题的研究：4He原子是否可能通过固体4He，如果可能，其机制是什么。其他人之前的工作表明，这种流动可能是可能的，更具体地说，可能存在一种超固体？在很低的温度下可能存在于固体4He中的物质状态。A？超级固体？将代表物质的一种新的量子态，因此它的存在问题引起了凝聚态社区的强烈兴趣，引发了许多实验和理论辩论，并产生了一些可能的解释和一些实质性的悖论。理论辩论坚持认为，完美的固体氦晶体不可能是超固态的，任何通过固体的质量流都必须由缺陷携带。各种缺陷机制已被提出。为了研究通过固体4He的质量流量的可能性，该项目将通过一种独特的技术在固体上施加化学势梯度：对与固体接触的液氦施加压差，而不是直接向4He晶格施加压力。这种方法利用了已知的4He的行为，在Vycor(一种多孔玻璃)中，在高压下保持液体，在压力下，4He是固体。在Vycor两侧的固体氦上施加化学势差将允许原子被注入到固体中，而不会对晶格施加机械压差。作为温度和压力函数的研究将提供(或不提供)流动的证据，并限制对流动负责的一套可能的机制。参与这些研究的学生将获得基础物理和尖端技术方面的经验。在完成博士学位论文后，他们将为工业、国家实验室和学术机构的科学研究和发展做出贡献。

****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.