Coexisting Bose & Fermi Superfluids and Fermi Liquid Transport in the Presence of Disorder

共存 Bose

• 批准号: 0202113
• 负责人: Jeevak Parpia
• 金额: $ 39万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-08-01 至 2006-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0202113&HistoricalAwards=false
• 关键词: Coexisting; Bose; Fermi; Superfluids; Liquid

This low temperature physics project will investigate the behavior of 3He, and phase-separated mixtures of 3He and 4He, in Aerogel. Aerogel, a dilute glass that occupies between 0.1% and 3% of the volume is the only means by which a structural "disorder" can be introduced to the 3He. One project will examine flow and the onset of dissipation (the breakdown of superfluidity) in this disordered superfluid. Magnetic resonance will be used to characterize the superfluidity of isolated "bubbles" of superfluid 3He trapped in the isotope mixtures. This will establish dimensional constraints that may limit superfluidity. These demanding experiments, which involve cutting edge instrumentation and development of new techniques, provide a challenging environment where graduate students and post-doctoral researchers acquire skills and analytic tools to prepare them for careers in the Nation's scientific and technological infrastructure.Liquid 3He, available only near "absolute zero" is one of the purest materials that can be prepared by any means. Impurities simply freeze out during the arduous cooling and liquefaction procedures required to obtain the liquid. Like its more abundant sister isotope 4He, 3He can be obtained in a "superfluid" state. But the superfluid is complicated by the magnetism of the 3He atoms, each of which acts like a tiny compass needle. The atoms themselves undergo mutual orbital motion, and their compass needles pair up in various ways depending on the orbital motion of the atoms. Because of its complex magnetic character, the superfluid properties of 3He are of fundamental interest, and in some circumstances can be related to more common phenomena like the flow of electrons in a wire. One project under this award will study how the ultra pure superfluid 3He changes when it is diluted and 'disordered' by the addition of Aerogel, a dilute glass that occupies less than 2% of the total volume of the container. The disorder introduced into the helium changes the orbital motions of 'paired' atoms, and in some conditions of temperature and pressure can destroy superfluidity altogether. The research will also look for changes in the pairing when the helium is confined to small "bubbles", which approximate a so-called zero-dimensional superfluid "dot". Finally the effects of fluid flow on the disordered superfluid will be examined with the objective of detecting energy dissipation, analogous to heating of a wire by current flow. This is signaled by loss of superfluidity. Besides adding to the understanding of quantum systems and superfluid flow, this research provides a demanding experimental environment that educates and trains graduate students and post-doctoral researchers for successful careers in the Nation's scientific and technological infrastructure.

该低温物理项目将研究 3He 以及 3He 和 4He 的相分离混合物在气凝胶中的行为。气凝胶是一种占体积 0.1% 到 3% 的稀玻璃，是向 3He 引入结构“无序”的唯一手段。一个项目将检查这种无序超流体中的流动和耗散（超流性的崩溃）。磁共振将用于表征同位素混合物中捕获的超流体 3He 的孤立“气泡”的超流动性。这将建立可能限制超流动性的尺寸约束。这些要求很高的实验涉及尖端仪器和新技术的开发，为研究生和博士后研究人员提供了一个具有挑战性的环境，让他们获得技能和分析工具，为他们在国家科技基础设施中的职业做好准备。液体 3He，仅提供接近“绝对零”是可以通过任何方式制备的最纯净的材料之一。 在获得液体所需的艰苦冷却和液化过程中，杂质会被冻结。 与其更丰富的姐妹同位素 4He 一样，3He 也可以在“超流体”状态下获得。 但超流体因 3He 原子的磁性而变得复杂，每个 3He 原子的作用就像一个微小的罗盘针。 原子本身进行相互的轨道运动，它们的罗盘针根据原子的轨道运动以各种方式配对。 由于其复杂的磁性特征，3He 的超流体特性引起了人们的根本兴趣，并且在某些情况下可能与更常见的现象（例如电线中的电子流动）相关。 该奖项下的一个项目将研究超纯超流体 3He 在通过添加气凝胶（一种占容器总体积不到 2% 的稀玻璃）进行稀释和“无序”时如何变化。 引入氦的无序改变了“成对”原子的轨道运动，并且在某些温度和压力条件下可以完全破坏超流动性。 该研究还将寻找当氦被限制在小“气泡”中时配对的变化，这些小“气泡”近似于所谓的零维超流体“点”。 最后，将检查流体流动对无序超流体的影响，目的是检测能量耗散，类似于电流对电线的加热。 这是超流动性丧失的标志。 除了增加对量子系统和超流体流动的理解之外，这项研究还提供了一个要求严格的实验环境，可以教育和培训研究生和博士后研究人员，以便他们在国家科技基础设施中取得成功的职业生涯。