Disordered 3He and Glassy Systems at mK Temperatures

该个人研究者奖支持一项实验计划，以研究低温下不同系统的无序性。将要研究的两个系统是：(i)气凝胶中的超流体3He，其中气凝胶引入了相关的无序；（ii）低温下的硅玻璃，其中声速和耗散为玻璃中无序的“标准隧道模型”的有效性提供了敏感的探针。该项目将使用超灵敏扭摆装置检查超流体3He的相位图，以了解“A”和“B”相发生时的滞后，钉住和各种磁场中的各向异性。he也将被用来进一步减小he的可达体积（最终变成孤立的“泡状”区域），同时保持超流动性。在二氧化硅玻璃上的实验将使用高Q谐振器来关注极低温行为（低于5mK），其中可能存在隧道位点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，发起，设计和实施的能力），并熟悉分析和显示工具，为他们在国家科学和技术基础设施的职业生涯做好准备。该研究项目还将包括一名本科生（全年）以及一名高中教师在夏季参与研究项目。%%%%%3He（不像所有其他元素）是一个固有的量子力学系统，它不会凝固（除非它被高度压缩），甚至降到绝对零度。它是可以用任何方法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被简单地冻结掉。最终he达到了一种高度有序的状态——超流动性，这与大多数超导体及其姊妹同位素he不同。超流体原子的磁性意味着原子成对在一起并进行轨道运动，表现出不同的相或“味道”。所有这些行为都受到气凝胶的影响，气凝胶是一种高度稀释的玻璃（也称为固化烟雾），其结构非常小，可以穿透超流体对，改变出现的超流体“味道”的发生（甚至可能是特征）。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。第二个领域探讨了我们对标准玻璃在低温下的性质的理解，在低温下，人们想象秩序是由于缺乏热激发而强加的。然而，玻璃表现出量子特性，原子从一种结构隧道到另一种结构，影响声音的传播质量。通过对这些系统进行精确测量，这项研究将增加我们对不太极端条件下无序作用的理解。除了增加对量子系统的理解之外，这项研究还提供了一个苛刻的实验环境，为国家科学和技术基础设施的成功职业生涯教育和培训研究生和本科生（并且还将通过让科学教师参与暑期研究计划产生积极影响）。

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.