Helium3 and Mixtures of Helium3/Helium4 in Aerogel, and High-Q Mechanical Detectors at Low Temperatures

9424131 Parpia这个项目探索了一维（气凝胶束）或零维（4 He原子）杂质对3 He超流性的影响。杂质的存在以不完全理解的方式改变了纯3 He的相图，并且经常令人惊讶。这项研究将使用纯3 He和3 He和4 He的混合物。 相当有趣的是3 He和4 He在混合物中的分布： 分离 可能会发生，其中一个 同位素 被优先吸附在附近的气凝胶胶体，超流体性质的系统可能会改变，等有可能的工作可能会导致发现的条件下，两种不同的超流体共存的混合物中的3 He和4 He。 这项工作将使用扭转振荡器和声共振器 到 绘制转变温度， 超流分数，声速和这些量子流体在气凝胶的热容。这项研究具有基础性， 提供有关 物理 超流体的行为。 这是一个实验性的低温物理项目。 该研究涉及由氦的同位素组成的超流液体：氦-3，氦-4或其混合物。氦-3或氦-4可以分别被冷却到超流体状态（粘度消失）。 最近，人们发现混合物 的 氦3和氦4 可以 有 这些超流体的性质与它们的母体超流体惊人地不同。 此外，已经发现，仅占样品体积的1%的多孔气凝胶（硅胶）“杂质”胶体的存在可以深刻地影响同位素混合物的超流体性质。这种效应与非常大的表面有关 气凝胶的面积。 一系列的低温技术正被用来研究这些超流体物理的基本问题。这些结果也可能与其他量子现象有关， 超导性。 ***

9424131 Parpia This project explores the effect of impurities that are one dimensional (strands of aerogel) or zero dimensional (4He atoms) on the superfluidity of 3He. The presence of impurities modifies the phase diagram of pure 3He in ways that are incompletely understood and are often surprising. The research will employ both pure 3He and mixtures of 3He and 4He. Of considerable interest is the distribution of 3He and the 4He in mixtures: Phase separation may occur, one of the isotopes being preferentially adsorbed near the aerogel colloid, the superfluid properties of the system may be changed, etc. There is the possibility that the work could lead to discovery of conditions in which two different superfluids coexist in a mixture of 3He and 4He. The work will use torsional oscillators and sound resonators to map the transition temperature, superfluid fraction, sound velocity and heat capacity of these quantum fluids in aerogels. The research is of a fundamental nature and will provide important information about the physics of superfluid behavior. %%% This is an experimental low temperature physics project. The research deals with superfluid liquids consisting of the isotopes of helium: helium-3, helium-4, or mixtures thereof. Separately, helium-3 or helium-4 can be cooled to the superfluid state (vanishing viscosity). Very recently, it was discovered that mixtures of helium-3 and helium-4 can have properties surprisingly different from the parent superfluids. Further, it has been found that the presence of a filamentary aerogel (a silica-gel) "impurity" colloid, which comprises only 1% of the sample volume, can profoundly affect the superfluid properties of the isotope mixtures. The effect is related to the very large surface area of the aerogel. A range of low temperature techniques are being employed to investig ate these fundamental problems, which bear of the physics of superfluids. The results may also be relevant to other quantum phenomena such as superconductivity. ***