Studies of Supersolid Phenomena in Solid Helium

凝聚态物理学最近最激动人心的发现之一就是在绝对零度以上零点几度的温度下观察到了所谓的“超固态”状态。这种超固态具有一个显著的特性，即只要温度足够低，一小部分氦固体实际上可以作为无摩擦流动通过自己。超固体的这种性质是违反直觉的，与我们对固体的本能概念不符。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4He和超流3He，超导电子，以及在低密度囚禁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，迄今所观察到的超固体现象是否是固体氦中存在真正的超流态的实际证据。这项研究项目将从两个方面解决这个问题。这种方法提出的问题是，超流体是否服从超流体流体动力学？第二种方法将利用最先进的超导技术，通过超灵敏的热容测量来检查向超固态相变的性质。这些项目将涉及几名本科生，并将使他们在科学研究中领先一步。*技术摘要*最近由EunSong Kim和Mosse Chan在低于200 MK的固体4He中发现了“超固态”相，这为四分之一个多世纪前的预测提供了现实。最初关于晶体4He处于超固态的建议是基于这样一种可能性，即在足够低的温度下，玻色-爱因斯坦凝聚可能在固体氦中发生。确定超固体状态是否代表一种新的超流体是至关重要的。这一个人调查员奖支持使用几种方法澄清这一问题的尝试。首先，超固体的流体动力学将在非圆形几何结构中进行检查，其中基于普通超流体流体动力学的预测行为是明确的。其次，将通过使用超灵敏SQUID技术测量与转变相关的可能的热容异常来解决实际到超固态状态的相变的问题。这个项目预计将涉及两名本科生，他们应该会从一个快速发展的领域中获益良多，该领域处于当前凝聚态研究的前沿。

****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.