Studies of Supersolid Phenomena in Solid Helium

****非技术摘要****在凝聚态物理学中，最近最令人兴奋的发现之一是在绝对零度之上仅零点几度的温度下观察到所谓的“超固体”状态。这种超固态有一个显著的特性，那就是只要温度足够低，一小部分氦固体就能以无摩擦的形式通过自身。超固体的这种特性是违反直觉的，与我们对固体的本能概念不一致。超固体可能是超流体系统的另一个例子，取代了先前已知的超流体；超流体4He和超流体3He，超导电子，以及在低密度捕获原子气体中观察到的超流体。必须解决的最重要的问题之一是，迄今观察到的超固体现象是否是固体氦中存在真正超流体状态的实际证据。这个研究项目将从两个方面解决这个问题。该方法提出了一个问题，超流体是否服从超流体流体力学？第二种方法将通过利用最先进的超导技术进行超灵敏热容测量来检查相变到超固态的性质。这些项目将涉及几名本科生，并将使他们在科学研究方面领先一步。****技术摘要****最近由Eunsong Kim和Moses Chan在低于200 mK的温度下在固体4He中发现了“超固体”相，实现了四分之一个多世纪前的预测。关于氦晶体中存在超固态的最初建议是基于在足够低的温度下固体氦中可能发生玻色-爱因斯坦凝聚的可能性。确定这种超固体状态是否代表一种新型的超流体是至关重要的。该个人研究者奖支持使用几种方法澄清这一问题的尝试。首先，超固体的流体力学将在非圆形几何中进行检验，其中基于普通超流体流体力学的预测行为是明确的。其次，将利用超灵敏的SQUID技术，通过测量与过渡相关的可能的热容异常，来解决实际相变到超固态的问题。该项目预计将涉及两名本科生，他们将从当前凝聚态研究前沿快速发展的领域中获益良多。

****NON-TECHNICAL ABSTRACT****One of the most exciting recent discoveries in condensed matter physics has been the observation of the so-called "supersolid" state at temperatures only a few tenths of a degree above absolute zero. This supersolid state has the remarkable property that a fraction of a helium solid can actually pass through itself as a frictionless flow provide the temperature is low enough. This property of the supersolid is counterintuitive and is at odds with our instinctive concept of a solid. The supersolid may be another example of a superfluid system to take its place beside the previously know superfluids; superfluid 4He and superfluid 3He, superconducting electrons, and the superfluids observed in low density trapped atomic gases. One of the most important questions that must be addressed is whether the supersolid phenomena thus far observed is actual evidence for a true superfluid state in solid helium. This research project will address this question on two fronts. The approach asks the question, does the superfluid obey superfluid hydrodynamics? The second approach will examine the nature of the phase transition to the supersolid state by an ultra sensitive heat capacity measurement utilizing state-of-the-art superconducting technology. These projects will involve several undergraduate students and will give them a head start in scientific research.****TECHNICAL ABSTRACT****The recent discovery of a "Supersolid" phase in solid 4He at temperatures below 200 mK by the Eunsong Kim and Moses Chan provides the realization of a prediction made more than a quarter of a century ago. The initial suggestion for a supersolid state in crystalline 4He is based on the possibility that Bose-Einstein condensation might occur in solid helium at sufficiently low temperatures. It is crucial to establish whether or not the supersolid state represents a new type of superfluid. This individual investigator award supports an attempt to clarify this issue using several approaches. First, the hydrodynamics of the supersolid will be examined in non-circular geometries where the predicted behavior based on ordinary superfluid hydrodynamics is clear. Second, the question of an actual phase transition to the supersolid state will be addressed through measurement of the possible heat capacity anomaly associated with the transition utilizing ultra sensitive SQUID technology. This project is expected to involve two undergraduate students who should profit greatly from working in a fast evolving area at the current forefront of condensed matter research.