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Intrinsic and dislocation-induced elastic behavior of solid helium

机译：固体氦的内在和位错诱导的弹性行为

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Recent experiments showed that the shear modulus of solid ~4He stiffens in the same temperature range (below 200 mK) where mass decoupling and supersolidity have been inferred from torsional oscillator measurements. The two phenomena are clearly related and crystal defects, particularly dislocations, appear to be involved in both. We have studied the effects of annealing and the effects of applying large stresses on the elastic properties of solid ~4He, using both acoustic resonances and direct low-frequency and low-amplitude measurements of the shear modulus. Both annealing and stressing affect the shear modulus, as expected if dislocations are responsible. However, it is the high-temperature modulus which is affected; the low-temperature behavior is unchanged and appears to reflect the intrinsic modulus of solid helium. We interpret this behavior in terms of dislocations which are pinned by isotopic ~3He impurities at low temperatures and so have no effect on the shear modulus. At higher temperatures they become mobile and weaken the solid. Stressing the crystal at low temperatures appears to introduce new defects or additional pinning sites for the dislocation network but these effects can be reversed by heating the crystal above 500 mK. This is in contrast to dislocations produced during crystal growth, which are only annealed at temperatures close to melting.
机译：最近的实验表明，在相同的温度范围（低于200 mK）下，固体〜4He的剪切模量会变强，在该温度范围内，已通过扭转振荡器测量得出了质量解耦和超固体。这两种现象显然相关，并且晶体缺陷，特别是位错，似乎都与这两种现象有关。我们使用声学共振以及剪切模量的直接低频和低幅测量，研究了退火的影响以及对固体〜4He的弹性特性施加大应力的影响。如位错所致，退火和应力都会影响剪切模量。但是，影响的是高温模量。低温行为没有改变，似乎反映了固体氦的固有模量。我们用位错来解释这种行为，这些位错在低温下被同位素〜3He杂质所钉扎，因此对剪切模量没有影响。在较高的温度下，它们变得可移动并削弱了固体。在低温下对晶体施加应力似乎会引入新的缺陷或位错网络的其他钉扎位点，但可以通过将晶体加热到500 mK以上来逆转这些影响。这与晶体生长过程中产生的位错相反，后者仅在接近熔化的温度下退火。

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