Shear Modulus and Dislocations in bcc Solid \(^3\) He

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• 作者：Zhi Gang Cheng ; Fabien Souris ; John Beamish
• 关键词：bcc solid \(^3\) ; He ; Shear modulus ; Dislocation
• 刊名：Journal of Low Temperature Physics
• 出版年：2016
• 出版时间：May 2016
• 年：2016
• 卷：183
• 期：3-4
• 页码：99-105
• 全文大小：1,128 KB
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• 作者单位：Zhi Gang Cheng (1)
  Fabien Souris (1)
  John Beamish (1)
  
  1. Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2E1, Canada
  
• 刊物类别：Physics and Astronomy
• 刊物主题：Physics
  Condensed Matter
  Characterization and Evaluation Materials
  Magnetism and Magnetic Materials
  
• 出版者：Springer Netherlands
• ISSN：1573-7357

文摘

The shear modulus of hcp \(^4\)He decreases significantly above \(\sim \)200 mK, as \(^3\)He impurities unbind from dislocations, unpinning them, and softening the crystal. Here we report shear modulus measurements on a fermi quantum solid: bcc \(^3\)He. In contrast to previous low-frequency measurements, which did not show dislocation softening in this system, we have observed a drop in shear modulus, accompanied by a dissipation peak, which we attribute to the unpinning of dislocations as \(^4\)He impurities unbind. For large stresses, impurities cannot pin the dislocations and the low temperature stiffening is suppressed. At high frequencies, the modulus changes and dissipation peaks shift to higher temperature, indicating that the unbinding is thermally activated. For a 58 bar bcc \(^3\)He crystal, we find an activation energy of 0.27 K, smaller than the 0.7 K binding energy for \(^3\)He impurities in hcp \(^4\)He.