Studies of Supersolid Phenomena in Helium and Hydrogen

* 非技术摘要 * 凝聚态物理学最近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可能观察到所谓的“超固体”状态。 这种超固态具有一个显著的特性，即只要温度足够低，一部分由氦组成的固体实际上可以作为无摩擦流通过自身。 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一致。 超固体是量子力学状态的另一个例子，被称为超流体，它与以前已知的超流体，超流体4 He和超流体3 He，超导电子以及在低密度捕获的原子气体中观察到的超流体一起。 超固态的可能发现是一个非常新的发现，希望有一个独立的确认这一现象。这个个人研究项目的第一个目标是提供这种确认。 下一步将是研究样品几何形状和晶体退火对超固体性质的影响。 退火实验特别有趣，因为最近的理论表明，在超固态出现之前，固体中需要一定程度的无序。 如果这是真的，那么超固体行为可能会通过退火过程消除，从而减少氦结晶固体中的无序量。 除了推进物质的量子力学状态的知识前沿，这项工作将为一名研究生提供培训。技术摘要 * Kim和Chan最近发现，在低于200 mK的温度下，固体4 He中存在一种潜在的“超固体”相，这使世纪前的一个预测得以实现。 最初对4 He晶体中超固态的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。 这个个人研究者奖支持一个旨在确认超固态存在并调查其性质的项目。 在原始实验的变化中，将使用立方几何中的扭转振荡器技术。 这确保了实体在几何上锁定到扭转振荡器，并且消除了在边界处滑动的可能性。 目前对超固态的理论理解表明，在理想的4 He hcp晶体中不会发生超固态现象，但固体中需要一定程度的无序。 因此，一个重要的研究将是检查晶体退火对任何观察到的超固体信号的影响。 这个项目将涉及一名研究生，他应该从目前凝聚态研究前沿的快速发展领域的工作中获益匪浅。

*****NON-TECHNICAL ABSTRACT*****One of the most exciting recent discoveries in condensed matter physics has been the possible 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 solid made of helium can actually pass through itself as a frictionless flow provided 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 is another example of a quantum mechanical state known as a superfluid and takes its place beside the previously known superfluids; superfluid 4He and superfluid 3He, superconducting electrons, and the superfluids observed in low-density trapped atomic gases. The possible discovery of the supersolid state is a very recent finding and it is desirable to have an independent confirmation of this phenomena. The first goal of this individual investigator project is to provide such confirmation. The next step will be to study the effects of sample geometry and crystal annealing on the properties of the supersolid. An annealing experiment is particularly interesting, since recent theories suggest that a degree of disorder is required in the solid before the supersolid state can appear. If this is true, then possibly the supersolid behavior might be removed by annealing process, which reduces the amount of disorder in the helium crystalline solid. In addition to advancing the frontier of knowledge of quantum mechanical states of matter, this work will provide training for one graduate student.***** TECHNICAL ABSTRACT*****The recent discovery of a potential "supersolid" phase in solid 4He at temperatures below 200 mK by Kim and 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. This individual investigator award supports a project aimed at confirming the existence of the supersolid state and investigating its nature. In a variation on the original experiment, torsional oscillator technique in a cubic geometry will be used. This ensures the solid is geometrically locked to the torsional oscillator and the possibility of slip at the boundary is eliminated. Current theoretical understanding of the supersolid state suggests that the supersolid phenomena will not occur in an ideal 4He hcp crystal but some degree of disorder in the solid will be required. Thus an important study will be examining the effects of crystal annealing on any observed supersolid signal. This project will involve one graduate student who should profit greatly from working in a fast evolving area at the current forefront of condensed matter research.