Journal
JOURNAL OF LOW TEMPERATURE PHYSICS
Volume 178, Issue 3-4, Pages 149-161Publisher
SPRINGER/PLENUM PUBLISHERS
DOI: 10.1007/s10909-014-1251-0
Keywords
Solid helium; Dislocations; Plasticity
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Funding
- European Research Council [AdG 247258-SUPERSOLID]
- Natural Sciences and Engineering Research Council Canada
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The giant plasticity of He crystals has been explained as a consequence of the large mobility of their dislocations. Thus, the mechanical properties of dislocation free crystals should be quite different from those of usual ones. In 1996-1998, Ruutu et al. published crystal growth studies showing that, in their helium 4 crystals, the density of screw dislocations along the c-axis was less than 100 per cm, sometimes zero. We have grown helium 4 crystals using similar growth speeds and temperatures, and extracted their dislocation density from their mechanical properties. We found dislocation densities that are in the range of 10-10 per cm, that is several orders of magnitude larger than Ruutu et al. Our tentative interpretation of this apparent contradiction is that the two types of measurements are somewhat indirect and concern different types of dislocations. As for the dislocation nucleation mechanism, it remains to be understood.
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