Disordered 3He and Glassy Systems at mK Temperatures

mK 温度下的无序 3He 和玻璃态系统

• 批准号: 0457533
• 负责人: Jeevak Parpia
• 金额: --
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-08-01 至 2010-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0457533&HistoricalAwards=false
• 关键词: Disordered; 3He; Glassy; Systems; mK

This individual investigator award supports an experimental program to investigate disorder in diverse systems at low temperatures. The two systems that will be studied are (i) superfluid 3He in aerogel, where the aerogel introduces correlated disorder and (ii) silica glass at low temperatures where the sound velocity and dissipation provide sensitive probes for the validity of the "standard tunneling model" of disorder in glasses. The project will examine the phase diagram of superfluid 3He for hysteresis in the occurrence of the "A" and "B" phases, for pinning, and for anisotropy in a variety of magnetic fields using ultrasensitive torsion pendulum devices. 4He will also be used to further reduce the volume accessible to the 3He (eventually into isolated "bubble-like" regions, while preserving superfluidity. The experiments on silica glass will use high Q resonators to focus on the very low temperature behavior (below 5mK) where there may be evidence of interactions between tunneling sites, as well as probe the non-linear behavior of these systems. These demanding experiments, which involve cutting edge instrumentation and development of new techniques, provide a challenging environment where graduate and undergraduate students acquire skills (the ability to innovate, initiate, design and carry out) as well as become familiar with analytic and display tools to prepare them for careers in the nation's scientific and technological infrastructure. The research program will also incorporate an undergraduate (year-round) as well as involve a high-school teacher in the research program during the summer. %%%%%3He (unlike all other elements) is in an inherently quantum-mechanical system that does not solidify (unless it is highly compressed) even down to absolute zero. It is one of the purest materials that can be prepared by any means, since at these temperatures, impurities simply freeze out during the procedures required to obtain the liquid state. Eventually 3He attains a highly ordered state - superfluidity, which is different from that attained in most superconductors and its sister isotope 4He. The magnetism of the superfluid atoms means that the atoms pair up together and undergo orbital motion exhibiting different phases or "flavors". All of this behavior is affected by introducing aerogel, a highly dilute glass (also termed solidified smoke) whose structure is so small that it penetrates into the superfluid pairs, altering the occurrence (and perhaps even the character) of the "flavors" of superfluid that appear. The research will look for changes under a variety of conditions, including when the helium is confined to small "bubbles". A second area probes our understanding of the properties of a standard glass at low temperatures, where one imagines that order is imposed by the absence of thermal excitations. However, the glass exhibits quantum characteristics, where atoms tunnel from one configuration to another, affecting the sound propagation qualities. By carrying out precise measurements on these systems the research will add to our understanding of the role of disorder under less extreme conditions. Besides adding to the understanding of quantum systems, this research provides a demanding experimental environment that educates and trains graduate and undergraduate students (and will also create a positive impact by involving a science teacher into the summer research program) for successful careers in the nation's scientific and technological infrastructure.

这个个人研究者奖支持一个实验计划，以调查在低温下不同系统的障碍。将研究的两个系统是（i）气凝胶中的超流3 He，其中气凝胶引入相关无序，以及（ii）低温下的二氧化硅玻璃，其中声速和耗散为玻璃中无序的“标准隧道模型”的有效性提供灵敏的探针。该项目将使用超灵敏度扭摆装置来检查超流3 He的相图，以研究“A”和“B”相发生时的滞后、钉扎以及各种磁场中的各向异性。4 He还将用于进一步减少3 He的体积（最终进入孤立的“气泡状”区域，同时保持超流性）。石英玻璃上的实验将使用高Q谐振器，专注于非常低的温度行为（低于5 mK），其中可能存在隧道位置之间相互作用的证据，以及探测这些系统的非线性行为。这些要求苛刻的实验，涉及尖端仪器和新技术的开发，提供了一个具有挑战性的环境，研究生和本科生获得技能（创新，启动，设计和执行的能力），以及熟悉分析和显示工具，为他们在国家的科学和技术基础设施的职业生涯做好准备。该研究计划还将纳入本科生（全年），以及涉及在夏季研究计划的高中教师。He（与其他元素不同）是一个固有的量子力学系统，即使在绝对零度下也不会凝固（除非它被高度压缩）。它是可以通过任何方式制备的最纯净的材料之一，因为在这些温度下，杂质在获得液态所需的过程中简单地冻结。最后，3 He达到一种高度有序的状态-超流性，这与大多数超导体及其姊妹同位素4 He所达到的状态不同。超流体原子的磁性意味着原子配对在一起并经历轨道运动，表现出不同的相位或“味道”。所有这些行为都受到引入气凝胶的影响，气凝胶是一种高度稀释的玻璃（也称为固化的烟雾），其结构非常小，可以渗透到超流体对中，改变出现的超流体“味道”的发生（甚至可能是特性）。这项研究将寻找各种条件下的变化，包括当氦被限制在小“气泡”中时。第二个领域探讨我们对标准玻璃在低温下的性质的理解，其中人们想象秩序是由热激发的存在所强加的。然而，玻璃表现出量子特性，其中原子从一种配置隧穿到另一种配置，影响声音传播质量。通过对这些系统进行精确的测量，这项研究将增加我们对在不那么极端的条件下无序作用的理解。除了增加对量子系统的理解外，这项研究还提供了一个苛刻的实验环境，可以教育和培训研究生和本科生（并通过将科学教师纳入夏季研究计划来产生积极影响），以在国家的科学和技术基础设施中取得成功。