Supersolidity and the Supersolid to Normal Solid Transition

超固体和超固体到普通固体的转变

• 批准号: 1103159
• 负责人: Moses Chan
• 金额: $ 92.5万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-08-01 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1103159&HistoricalAwards=false
• 关键词: Supersolidity; Supersolid; Normal; Solid; Transition

Technical Abstract.The observation of superfluid-like behavior in bulk solid helium and solid helium confined in porous media in the P.I.'s laboratory has been replicated in a dozen other laboratories. Quantum Monte Carlo simulations suggest superfluidity is not possible in a perfect crystal but dislocation lines may be superfluid. Shear modulus measurements indicate that superfluidity in solid helium or supersolidity is the consequence of a stiffened network of interconnected dislocation lines. This model however, cannot explain the results in porous media since it is difficult to envision dislocation lines inside a pore of a few nm. Three questions will be addressed in this project. One set of experiments will determine if supersolidity is possible in a perfect crystal with little or no dislocation lines. Secondly, heat capacity, thermal conductivity measurements will be carried out to determine how supersolidity in porous media is different from that in bulk solid. Lastly torsional oscillator measurements will be made to determine the spatial extent of quantum phase coherence in a supersolid system. The experiments are exceptionally challenging hence providing an excellent training ground for the post-doctoral, graduate and undergraduate students in the project. The P.I. has a very strong and sustained record in training students for successful scientific careers in academia and in industrial and government laboratoriesNon-technical AbstractWhen liquid helium is cooled below -271 Celsius, or 2 K above absolute zero, it enters the superfluid state with zero viscosity allowing it to flow relative to the walls of a container with no friction. What this means is that if a container is being oscillated back and forth, the superfluid inside will sit perfectly still. Like superconductivity, superfluidity is a manifestation of quantum mechanics at macroscopic scales. In 2004, the P.I. and one of his former student found evidence that below 0.2K, a small fraction (on the order of 1%) of a solid helium sample would remain stationary when its container is being oscillated. This experiment, since replicated in a dozen laboratories worldwide, indicates the existence of superfluidity in a solid, more conveniently called supersolidity. The discovery of this new state of matter has created considerable excitement in the physics community and beyond. An outstanding question of the phenomenon is whether supersolidity is possible in a perfect helium crystal or it requires the presence of defects such as dislocation lines in the crystal. The experiments proposed in the project are designed to resolve this question and will be carried out by post-doctoral, graduate and undergraduate students. The P.I. has a very strong and sustained record in training students for successful scientific careers in academia, industrial and government laboratories.

技术摘要：在P.I.S实验室观察到的块状固体氦和限制在多孔介质中的固体氦中的类超流体行为已经在其他十几个实验室中重复进行。量子蒙特卡罗模拟表明，完美晶体中不可能存在超流，但位错线可能是超流的。剪切模量值的测量表明，固体氦中的超流动性或超固体是由相互连接的位错线组成的加劲网络的结果。然而，这个模型不能解释多孔介质中的结果，因为很难想象几纳米的孔洞内有位错线。在这个项目中将解决三个问题。一组实验将确定在没有位错线或很少位错线的完美晶体中是否存在超固态。其次，将进行热容、导热系数的测量，以确定多孔介质中的超稠度与散体固体中的超稠度有何不同。最后，将通过扭转振子测量来确定超固体系统中量子相位相干性的空间范围。这些实验极具挑战性，因此为该项目的博士后、研究生和本科生提供了一个极好的培训场所。在为学术界以及工业和政府实验室的成功科学生涯培养学生方面，P.I.有着非常强大和持久的记录非技术摘要当液氦冷却到零下271摄氏度或绝对零度以上2K时，它进入超流状态，粘度为零，允许它相对于容器的壁面无摩擦地流动。这意味着，如果一个容器来回摆动，里面的超流体将完全静止不动。和超导一样，超流性也是量子力学在宏观尺度上的一种表现。2004年，P.I.和他以前的一名学生发现了证据，在0.2K以下，当固体氦样品的容器振荡时，一小部分(约1%)固体氦样品将保持不变。这项实验已经在世界各地的十几个实验室中重复进行，表明固体中存在超流动性，更方便的说法是超固体。这种新的物质状态的发现在物理学界和更远的地方引起了相当大的兴奋。这一现象的一个悬而未决的问题是，在完美的氦晶体中是否可能存在超固态，或者它是否需要晶体中存在诸如位错线之类的缺陷。该项目中提出的实验就是为了解决这个问题，将由博士后、研究生和本科生进行。在培养学生在学术界、工业和政府实验室取得成功的科学生涯方面，P.I.有着非常强劲和持久的记录。