Experiments in Quantum Solid He-4

实验证据表明，量子固体He-4部分地从其移动的容器壁机械地分离。 对这些实验的一个令人兴奋但有争议的解释是，量子固体He-4在保持其晶体性质的同时表现出超流体的行为。 人们普遍认为，存在的缺陷，如位错线和晶界在某种程度上涉及。 在这个项目中，将进行实验来测量超声传播（用于探测缺陷）和扭转振荡（用于探测机械解耦），同时测量固体He-4的相同样品，以阐明这两种效应之间的关系。 第四种声音，只有当材料成为超流体时才能在材料中传播，将被搜索。 第四声传播的成功观测将为固体He-4的超流性提供有力的证据。 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，数据采集和分析的现代技术。非技术摘要了解量子力学如何影响固体的物理性质是固体物理领域最重要的目标之一。 通过原子的离域或“离域”程度来衡量，在非常低的温度下，固态氦是自然界中已知的最受量子力学影响的物质。 因此，在基础物理学和最终材料利用方面，获得固体氦性质的全面知识至关重要。 利用高频超声传播技术对氦的内部结构如缺陷和晶体缺陷进行无损测量。 这种超声探头将通过测量同一固体对附着在其表面的移动物体的机械响应来补充。 这两种测量的比较旨在揭示固体氦以及最终具有技术重要性的其他固体的量子力学行为的起源。 该项目中令人兴奋的基础研究将由参与的本科生和研究生以及博士后研究员体验。 所有参与者将接触到仪器，数据采集和分析的现代技术。 研究经验将是一个很好的训练场，为成为美国科学工作力量的一部分做准备。

Technical AbstractExperimental evidence has shown that the quantum solid He-4 partially decouples mechanically from its moving container wall. An exciting yet controversial interpretation of these experiments is that the quantum solid He-4 behaves as a superfluid while retaining its crystalline properties. It is generally agreed that the presence of defects such as dislocation lines and grain boundaries is somehow involved. In this project, experiments will be carried out to measure both ultrasonic propagation (for probing the defects) and torsional oscillation (for probing mechanical decoupling) will be simultaneously measured in the identical sample of solid He-4 in order to elucidate the relationship between these two effects. Fourth sound, which propagates in a material only if the material becomes a superfluid, will be searched. A successful observation of fourth sound propagation will supply a definitive evidence for superfluidity of solid He-4. 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.Non-Technical AbstractUnderstanding how quantum mechanics affects the physical properties of solids is one of the most important goals of solid state physics field. Measured by the degree of delocalization or "fuzziness" of atoms, solid helium at very low temperatures is the substance known in nature most affected by quantum mechanics. It is then crucial in fundamental physics and ultimately in utilization of materials to acquire thorough knowledge of the properties of solid helium. The internal structure such as defects and crystalline faults in solid helium will be measured by non-destructive high frequency ultrasound propagation techniques. This ultrasound probe will be complemented by the measurement of the mechanical response of the same solid to a moving body attached to its surface. Comparison of these two measurements is designed to reveal the origins of quantum mechanical behavior of solid helium and ultimately other solids of technological importance. The exciting fundamental research in the project will be experienced by participating undergraduate and graduate students as well as postdoctoral fellows. 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.