Studies of Supersolidity in Solid 4He

固体 4He 中超固态的研究

• 批准号: 1206215
• 负责人: John Reppy
• 金额: $ 43.5万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-06-01 至 2019-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1206215&HistoricalAwards=false
• 关键词: Studies; Supersolidity; Solid; 4He

****Technical Abstract****The recent discovery of a "supersolid" phase in solid 4He at temperatures below 200mK 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. In an attempt to clarify this issue several approaches will be pursued. 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, multiple frequency compound oscillators will be used to distinguish a true superfluid from effects arising from the anomaly, discovered by Day and Beamish, in the low temperature properties of the elastic shear modulus. Third, the question of the existence of a thermodynamic phase transition to the supersolid state will be addressed through measurement of the expected heat capacity anomaly associated with the transition utilizing ultra sensitive SQUID technology. This project is expected to involve one to two undergraduate students who should profit greatly from working in a fast evolving area at the current forefront of condensed matter research.****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 3He and 4He, superconducting electrons, and the superfluids observed in low density trapped atomic gases. One of the most important questions to be addressed is whether the supersolid phenomena thus far observed is actual a true superfluid state in solid helium or is it a manifestation of the unusual elastic properties of the solid know to appear in the same temperature region as the supersolid phenomenon. This research project will address this question on several fronts. The approach asks the question, does the superfluid obey superfluid hydrodynamics and can the effects of elasticity be separated from those of a superfluid by multi-frequency experiments? The second approach will examine the nature of the phase transition to the supersolid state by a 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.

*技术摘要*金恩松和陈摩西最近在固体4He中发现了温度低于200mK的“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。为了澄清这一问题，将采取几种办法。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，多频复合振荡器将被用来区分真正的超流体和由Day和Beamish发现的异常引起的影响，这些异常是在弹性剪切模数的低温属性中产生的。第三，通过利用超灵敏SQUID技术测量与转变相关的预期热容异常，将解决热力学相变到超固态状态的存在的问题。这个项目预计将有一到两名本科生参与，他们将从当前凝聚态研究前沿快速发展的领域中受益匪浅。凝聚态物理学最令人兴奋的发现之一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，它取代了以前已知的超流体：3He和4He超流，超导电子，以及在低密度囚禁原子气体中观察到的超流体。要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真的是固体氦中的一种真正的超流体状态，或者它是已知出现在与超固体现象相同的温度区域的固体不同寻常的弹性性质的表现。这项研究项目将从几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，弹性效应能否通过多频率实验从超流体中分离出来？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方面领先一步。