Fourth Sound Propagation in Supersolid Helium 4

*非技术抽象*刚性固体表现为超流体，可以无摩擦流动，这可能看起来非常奇怪。尽管如此，理论上已经预测到这种“超固体”的存在。之前所有寻找这种固体的尝试都失败了。最近，用一种特殊的含有加压固体氦-4的圆柱摆进行的实验表明，固体显然部分地从容器壁上分离出来。一种令人兴奋但有争议的解释是，这些实验为人们长期寻求的超固体提供了证据。如果这一解释得到证实，它将呈现一种关于物理固态的全新观点。因此，为超固体提供一个独立和确凿的证据是至关重要的。当且仅当物质成为超流体时，一种独特的波传播被称为“第四声”才能在物质中传播。该项目将在超低温下寻找这样的波在固体氦-4中的传播。如果发现该波，将确认氦-4中的超固体。它将成为测量这种有趣材料性质的新的探索器，开辟了固体物理的一个新领域。参与该项目的本科生和研究生以及博士后研究员将体验基础研究的兴奋。所有参与者都将接触到仪器、数据采集和分析方面的现代技术。这一研究经验将是为成为美国科学工作队伍的一部分做准备的极好的训练基础。*技术摘要*最近对低于200MK的量子固体He-4进行的扭转振荡器实验表明，该固体与其移动的容器壁部分解耦。对这些实验的一种令人兴奋但有争议的解释是，固体He-4在保持其结晶性质的同时，表现为超流体。在本项目中，我们将利用超导量子干涉装置技术，在低温固体He-4中寻找新的第四声波传播。第四，当且仅当物质变成超流体时，声音才能在物质中传播。第四声传播的成功观测将为固体He-4的超流性提供确凿而重要的证据。它将为测量超流体分数、热性能和机械性能提供一个独立的探头。研究生和博士后研究员将参与现代凝聚态物理学的真正前沿研究。本科生将作为荣誉和独立项目参与研究。他们都将接触到仪器、数据采集和分析方面的现代技术。

****NON-TECHNICAL ABSTRACT****It might seem extremely odd that a rigid solid behaves as a superfluid, which can flow without friction. Nevertheless, such a "supersolid" has been theoretically predicted to exist. All prior attempts to find such a solid have failed. Recently, experiments with a special cylindrical pendulum containing pressurized solid helium-4 showed that the solid apparently partially separates from its container wall. An exciting but controversial interpretation is that the experiments provide evidence for the long-sought supersolid. If the interpretation is confirmed, it presents an entirely new view of the physical solid state. It is thus of paramount importance to furnish an independent and conclusive proof for supersolidity. A unique wave propagation known as "fourth sound" can propagate in a material if and only if it becomes a superfluid. This project will search for just such wave propagation in solid helium-4 at ultra low temperatures. If the wave is found, the supersolidity in helium-4 will be confirmed. It will then become a new probe for measuring the properties of this interesting material and open up a new field of solid state physics. The undergraduate and graduate students as well as postdoctoral fellows participating in this project will experience the excitement of fundamental research. All participants will be exposed to the modern technologies in instrumentation, data acquisition and analyses. The research experience will be an excellent training ground in preparation for becoming a part of scientific work force in the U.S.**** TECHNICAL ABSTRACT****Recent torsional oscillator experiments on the quantum solid He-4 below 200 mK indicate that the solid partially decouples from its moving container wall. An exciting but controversial interpretation of these experiments is that the solid He-4 behaves as a superfluid while retaining its crystalline properties. In this project, new fourth sound wave propagation will be searched for in the low temperature solid He-4 using the techniques of superconducting quantum interference device. Fourth sound can propagate in a material if and only if the material becomes a superfluid. A successful observation of fourth sound propagation will supply the definitive and important proof of superfluidity of solid He-4. It will provide an independent probe for measuring the superfluid fraction, thermal and mechanical properties. Graduate students and postdoctoral fellows will participate in a truly frontier research of modern condensed matter physics. Undergraduate students will be involved in the research as honors and independent projects. They will all be exposed to the modern technologies in instrumentation, data acquisition and analyses.