固体4 He和超固相：从理论推测到新物质态的发现？研究的历史与现状述评
Solid 4He and the Supersolid Phase: from Theoretical Speculation to the Discovery of a New State of Matter? A Review of the Past and Present Status of Research
摘要：
超固态物质的可能性，即，一种表现出超流体性质的晶体固体，大约四十年前首次出现在理论研究中。由于缺乏实验证据，在很长一段时间内没有什么兴趣之后，自从Kim和Chan（宾夕法尼亚州立大学，美国）报告了固体4 He样品中非经典转动惯量效应的证据以来，它在过去几年中引起了强烈的实验和理论关注。自从这个“第一次观察”以来，其他实验组已经观察到了这种效应对晶体氦样品旋转的响应，并且很明显，固体的响应对生长条件，退火过程和3 He杂质非常敏感。在相同的温度范围内的比热峰值已被报道，以及异常的弹性行为的固体4 He与扭转振荡器实验所揭示的现象具有很强的相似性。最近，在hcp固体4 He中观察到不寻常的质量输运也被报道，这表明超流。从理论上讲，固体~ 4 He的研究已经采用了强有力的模拟方法，但数据的解释仍然相当困难;处理超固体问题意味着人们不仅要面对量子相干性现象和晶体有序共存的问题，探索自发对称性破缺和量子场论的领域，也是无序的作用的问题，即，缺陷如空位、杂质、位错和晶界如何参与相变机制。
英文摘要：
The possibility of a supersolid state of matter, i.e., a crystalline solid exhibiting superfluid properties, first appeared in theoretical studies about forty years ago. After a long period of little interest due to the lack of experimental evidence, it has attracted strong experimental and theoretical attention in the last few years since Kim and Chan (Penn State, USA) reported evidence for nonclassical rotational inertia effects, a typical signature of superfluidity, in samples of solid 4He. Since this "first observation", other experimental groups have observed such effects in the response to the rotation of samples of crystalline helium, and it has become clear that the response of the solid is extremely sensitive to growth conditions, annealing processes, and 3He impurities. A peak in the specific heat in the same range of temperatures has been reported as well as anomalies in the elastic behaviour of solid 4He with a strong resemblance to the phenomena revealed by torsional oscillator experiments. Very recently, the observation of unusual mass transport in hcp solid 4He has also been reported, suggesting superflow. From the theoretical point of view, powerful simulation methods have been used to study solid 4He, but the interpretation of the data is still rather difficult; dealing with the question of supersolidity means that one has to face not only the problem of the coexistence of quantum coherence phenomena and crystalline order, exploring the realm of spontaneous symmetry breaking and quantum field theory, but also the problem of the role of disorder, i.e., how defects, such as vacancies, impurities, dislocations, and grain boundaries, participate in the phase transition mechanism.
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