Pinning Mechanism of the Dislocation Lines in bcc Solid 3He

Abstract

The strain amplitude dependence of the energy dissipation and the shear modulus at several temperatures are measured in bcc solid ³He and the results are compared with the model of a pinned dislocation loop of Granato and Lücke. In spite of the pure solid, the strong amplitude dependence of the dissipation is found in bcc solid ³He by the high-Q torsional oscillator measurements, in contrast with the result of the ultrasonic and the torsional-oscillator measurements in hcp solid ⁴He. In pure solids, the loop length of the dislocations cannot be limited by impurities. In order to clarify a pinning mechanism, the loop length and the network length are obtained from the experimental result by using the model of Granato and Lücke. Where, the loop length is determined by the pinning centers, and the network length is limited by the dislocation network nodes. It is found that the temperature dependence of the loop length is the same as that of the network length. This result shows that the pinning centers are the network nodes of the dislocation lines in ultra pure bcc solid ³He.