SGER: Superfluid State of Solid Helium Four

最近的扭转振荡器实验表明，第一个可能的证据表明，固体He-4在230MK以下具有超流性。现在至关重要的是，要对超流现象提供一个独立而明确的实验验证。在这项SGER计划中，我们计划探索第四声在固体He-4中的传播。第四，只有当物质变成超流体时，声音传播才会发生，而对它的观察构成了超流体的确凿证据。建议使用超导薄膜测辐射热计在固体He-4中进行第一次这样的搜索。当固体氦转变为超流体时，预计会有一个与之相关的比热信号。在与陈教授的团队(宾夕法尼亚州立大学)的合作下，罗格斯大学也将测量固体He-4的比热到5MK。固体He-4中的超流性会影响其力学性能，如对外加应力的响应。文中还提出了超固化度对液固界面应力驱动不稳定性现象的影响。所有三个拟议的实验都是有风险的，因为超固体相的行为在很大程度上是未知的。结果的影响将是巨大的：它将在实验和理论上开辟一个新的研究领域，研究低温下“超固体”背后的基本物理机制。拟议的研究将向本科生、毕业生和研究生展示和培训低温物理基础研究的先进原理和技术。拟议基础研究的经验将为年轻科学家为他们未来在学术界、工业界和整个社会的职业生涯奠定智力基础。固体有可能像没有粘度一样流动吗？根据最近进行的一项实验，答案是肯定的。该实验是在非常低的温度下测量固体氦四的转动惯量，仅比绝对零度高出零点几度。现在至关重要的是，对固体氦的超流性提供一个独立和独特的实验验证。通过一系列研究，这个SGER项目试图证明或反驳“超固体氦”的存在。超固态(或其他)的确凿证据的影响将是巨大的：它将在实验和理论上开辟一个新的研究领域，研究低温下“超固态”背后的基本物理机制。当我们理解这一新现象时，改善和控制材料的性能，如摩擦、粘合和流动，应该是可能的。因此，这些研究对基础科学和最终的技术进步具有潜在的广泛和重要的影响。该项目将试图通过寻找第四种声音传播来给出固体氦四的超流性的独立证据，除非物质是超流体，否则不会发生第四种声音传播。第四种声音是声波，在这种声波中，只有超流部分运动，其余的固体处于静止状态。对第四次声音传播的观察将为超流现象提供确凿的证据。该项目的另一部分是测量低至0.005 K的固体氦4的热容，以寻找超流体转变的热力学特征。拟议的研究将向本科生、毕业生和研究生展示和培训低温物理基础研究的先进原理和技术。在拟议的基础研究方面的经验将为年轻科学家为他们未来在学术界、工业界和整个社会的职业生涯奠定智力基础。

Recent torsion oscillator experiments showed the first probable evidence of superfluidity of solid He-4 below 230 mK. It is now crucial to provide an independent and distinct experimental verification of the superfluidity. In this SGER project, it is proposed to search for propagation of fourth sound in solid He-4. Fourth sound propagation occurs only if the material becomes superfluid and the observation of it constitutes an unmistakable proof of superfluidity. It is proposed to conduct the first such search in solid He-4 using a superconducting film bolometer. When solid helium transforms into a superfluid, an associated signature in specific heat is expected. In collaboration with Prof. Chan's group (Pennsylvania State University), the specific heat of solid He-4 will also be measured down to 5 mK at Rutgers University. The superfluidity in solid He-4 should affect its mechanical properties such as its response to externally applied stress. It is also proposed to search for the influence of supersolidity on the phenomenon of stress-driven instability at the liquid solid interface. All three proposed experiments are risky since the behavior of the supersolid phase is largely unknown. The impact of the results will be enormous: it will open up a new field of research in both experiment and theory to study the fundamental physical mechanism behind the "supersolidity" at low temperatures. The proposed research will expose and train undergraduates, graduates and post-graduates in the advanced principles and technologies in fundamental research in low temperature physics. The experience in the proposed basic research will lay the intellectual foundation for the young scientists in preparation for their future careers in academia, industries and society at large.%%%Is it possible that a solid can flow as if it has no viscosity? The answer is affirmative according to the recent experiment carried out to measure the rotational inertia of solid helium four at very low temperatures, just a few tenths of a degree above the absolute zero temperature. It is now crucial to provide an independent and distinct experimental verification of the superfluidity of solid helium. Through a series of studies, this SGER project attempts to prove or disprove the existence of "supersolid helium." The impact of corroborative proof of supersolid (or otherwise) will be enormous: it will open up a new field of research in both experiment and theory to study the fundamental physical mechanism behind the "supersolidity" at low temperatures. When we understand this novel phenomenon, improvements and control of materials properties such as friction, adhesion, and flow, should become possible. Thus, these studies have potentially broad and important impacts on fundamental science as well as eventual technological advancement. The project will attempt to give an independent proof of superfluidity of solid helium four by searching for the fourth sound propagation, which would not occur unless the material is a superfluid. The fourth sound is the acoustic wave in which only the superfluid fraction moves leaving the rest of solid at rest. Observation of the fourth sound propagation will provide an unmistakable proof of superfluidity. Another part of the project is to measure the heat capacity of solid helium four down to 0.005 K in search of thermodynamic signature of the superfluid transition. The proposed research will expose and train undergraduates, graduates and post-graduates in the advanced principles and technologies in fundamental research in low temperature physics. The experience in the proposed basic research will lay the intellectual foundation for the young scientists in preparation their future careers in academia, industries and society at large.