QFS2016 Book of Abstracts

Abstracts

O2.5 Nonlinear ultrasound propagation in solid 4 He due to pinning and unpinning of dislocations by 3 He Iwasa I.(1), Kojima H.(2) 1) Faculty of Science, Kanagawa University, Kanagawa, Japan 2) Serin Physics Laboratory, Rutgers University, New Jersey, USA Ultrasound attenuation ( α ) and velocity (v) at 9.6MHz are measured in polycrystalline hcp 4 He. Ultrasound signal above 200mK is linear and understood in terms of resonant vibration of dislocation segments pinned at network nodes with average pinning length (4.5 µ m), much shorter than that from shear modulus (59 µ m). Dramatic changes in α and v are observed below 200mK. The changes are strongly dependent on temperature, nonlinear and hysteretic. These effects result from pinning and unpinning of dislocations by 3 He impurities (0.3ppm). The dislocation damping constant due to thermal phonons, the binding energy between dislocation and 3 He, and the stress-induced unpinning process are analysed.

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