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

9424131这个项目探索了一维杂质(气凝胶)或零维杂质(4He原子)对3He超流性的影响。杂质的存在改变了纯3He的相图，这种方式还不完全被理解，而且经常令人惊讶。这项研究将使用纯3He和3He和4He的混合物。值得关注的是3He和4He在混合物中的分布：可能发生相分离，其中一种同位素优先吸附在气凝胶胶体附近，体系的超流体性质可能发生改变等。这项工作有可能导致发现两种不同的超流体在3He和4He混合物中共存的条件。这项工作将使用扭转振荡器和声谐振器来绘制气凝胶中这些量子流体的转变温度、超流体比例、声速和热容量。这项研究具有基础性，将提供有关超流体行为物理的重要信息。这是一个实验性的低温物理项目。这项研究涉及由氦的同位素组成的超流体液体：氦-3、氦-4或其混合物。另外，氦-3或氦-4可以冷却到超流体状态(粘度消失)。最近，人们发现氦-3和氦-4的混合物具有与母体超流体惊人的不同性质。此外，人们还发现，只占样品体积1%的丝状气凝胶(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。这种影响与气凝胶非常大的表面积有关。一系列低温技术正被用来研究这些与超流体物理有关的基本问题。这一结果也可能与超导等其他量子现象有关。***

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. ***