This article reviews experiments on elasticity, plasticity and ow of solid 4He and 3He, focusing on dislocations and other defects that are responsible for the unusual mechan-ical behavior of such quantum crystals. Heliums zero point motion prevents it from freezing unless pressure is applied, and makes the solid extremely compressible, with elastic constants orders of magnitude smaller than those of conventional solids. Tunnel-ing allows defects to remain mobile at low temperatures so dislocations have much larger eects on mechanical properties than in conventional solids. At temperatures below 400 mK, dislocations in hcp 4He are essentially undamped and, in the absence of pinning by 3He impurities, glide freely in the basal plane. In this regime, dislocation motion reduces the shear modulus by as much as 90%, an eect that has been referred to as giant plasticity although it is reversible and so might be better described as soften-ing. In this low temperature regime, macroscopic plastic deformation occurs via sudden dislocation avalanches with a wide range of time and length scales. At higher temper-atures, dislocation motion is damped, introducing dissipation in elastic measurements, and thermally activated defect motion makes helium crystals extremely ductile, owing under millibar stresses near melting. During the last decade, most of the properties of the dislocations that are responsible for the elastic eects described in this review have been accurately measured: their orientation, density and length distributions, the nature of their networks, and their binding to isotopic impurities. Despite this detailed understanding of mobile dislocations, there remain open questions. Much less is known about defects roles in the elastic and plastic behavior of hcp and bcc 3He crystals and even in hcp 4He, almost nothing is known about other types of dislocations that are immobile and so do not aect elastic properties. These might be responsible for recently observed superuid-like mass ow in 4He at low temperatures, although it is now clear that the apparent mass decoupling seen in torsional oscillator experiments with solid 4He was due to the elastic eects described in this paper, not to supersolidity.

中文翻译：

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固体氦的机械行为：弹性，可塑性和缺陷

本文回顾了关于固体4He和3He的弹性，可塑性和流动性的实验，重点研究了导致这种量子晶体异常机械行为的位错和其他缺陷。氦零点运动可防止其冻结，除非施加压力，并且使固体具有极高的可压缩性，其弹性常数比常规固体小几个数量级。隧穿可使缺陷在低温下保持可移动状态，因此位错对机械性能的影响比常规固体中的影响大得多。在低于400 mK的温度下，hcp 4He中的位错基本上没有阻尼，并且在没有3He杂质钉扎的情况下，其在基面上自由滑动。在这种情况下，位错运动会使剪切模量降低多达90％，尽管这种可逆性是可逆的，但它被称为巨大的可塑性，因此可以更好地描述为软化。在这种低温条件下，宏观塑性变形是通过突然错位的雪崩发生的，时间和长度范围很广。在较高的温度下，位错运动受到阻尼，从而在弹性测量中引入了耗散，并且由于在接近毫巴的应力下熔化，热激活的缺陷运动使氦晶体极具延展性。在过去十年中，已准确测量了导致本评价中描述的弹性变形的位错的大多数特性：其方向，密度和长度分布，其网络的性质以及它们与同位素杂质的结合。尽管对移动性脱位有详尽的了解，还有悬而未决的问题。关于缺陷在hcp和bcc 3He晶体的弹性和塑性行为中所起的作用知之甚少，甚至在hcp 4He中，对于固定的其他类型的位错也几乎一无所知，因此不会影响弹性。这些可能是最近在低温下观察到的4He超流体状质量流的原因，尽管现在很明显，在扭转振动器实验中，固体4He的表观质量解耦是由于本文所述的弹性效应引起的，而不是由于超固相。