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CAMP Seminar: Resonance-Type Ultrasound Attenuation in Solid Helium and Superconductors due to Dislocations

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Izumi Iwasa, Kanagawa University
When
28 March 2017 from 3:30 PM to 4:30 PM
Where
339 Davey Laboratory
Contact Name
Chaoxing Liu
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Dislocations play important roles in affecting the mechanical properties of crystalline materials and the ultrasound in MHz range is a sensitive tool to study dislocations.  The ultrasound techniques together with the theory of dislocation vibration were applied to the quantum solid helium at temperatures down to 15 mK and to the analysis of ultrasound attenuation in superconducting tin.  In solid helium samples, the dislocation density and the average segment length are extracted from analyzing the more than 20-dB increase in attenuation from 1.5 K to 0.3 K due to the decrease in thermal damping of the dislocation motion.  Similar phenomenon occurs in superconducting tin below Tc owing to the decrease in damping due to normal electrons.  In both cases the mode of dislocation vibration transforms from overdamped- to underdamped-resonance as the damping constant is lowered.  Below 0.3 K the attenuation in solid helium becomes amplitude-dependent and hysteretic.  We have identified the origin of the effects as pinning of dislocations by 3He impurities and determined the binding energy.

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