Migration of 3He impurities along dislocation lines in 4He single crystals

Abstract

We have studied acoustic resonances in 4He single crystals in the temperature region 20 < T < 300 mK where a large softening occurs due to the unbinding of dislocations from 3He impurities. Here we present an analysis of the dependence of resonance frequencies on the sound amplitude, that is on the acoustic stress in the crystal. Above a threshold of order 10−6 bar, this stress is able to unbind dislocations from impurities. Our results indicate that 3He impurities diffuse along dislocations at 60 mK but not at 23 mK.