Acoustic Properties of Solid 4He in the Limit of Zero Impurity
نویسندگان
چکیده
We have studied the elasticity of solid 4He in relation with its possible supersolidity. For this we have measured acoustic resonance frequencies in a 1 cm3 cell filled either with polycrystals or with single crystals of 4He. We have observed a large stiffening at low temperature as first observed by Day and Beamish in polycrystals. The 3He impurity content has been varied from 300 ppb to 0.4 ppb. When kept in equilibrium with liquid helium, single crystals should be impurity free. In these crystals, a large stiffening is observed, which should not be the result of the pinning of dislocations by impurities.
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