QFS 2016 Book of Abstracts

Abstracts

O2.2 Defect motions in quantum solids with spins Cheng Zhi-Gang, Beamish John Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1 Canada Defect motion in solid helium has uniquely quantum nature due to the large zero-point motion of helium atoms. Dislocations in solid 4 He are strongly pinned by 3 He impurities at low temperature but extremely mobile at high temperature, causing the shear modulus greatly reduced. 3 He has even larger zero-point motion than 4 He and extra nuclear spins, which may govern defect motion differently. We report shear modulus measurements of hcp solid 3 He to explore its dislocation motion. We observed the crossover between stiff and soft states due to 4 He impurities immobilizing dislocations as static pinning sites, as well as dissipation strongly depending on frequency. Both suggest the coupling between spin system and dislocation motion. We also observed extra softening at high temperature that does not exist for solid 4 He. O2.3 Experiments with Flow through a 4 He Solid-Filled Cell Valentyn Rubanskii, R.B. Hallock University of Massachusetts Amherst Department of Physics Amherst, MA 01003 USA Torsional oscillator results with solid 4 He initially pointed to the presence of a supersolid. Current evidence suggests that most of these torsional oscillator results were instead due to mechanical properties of the solid. Meanwhile, experiments at the University of Massachusetts demonstrated flow of helium through a solid-filled cell. A number of the Massachusetts observations have recently been confirmed in another laboratory. The flow has a variety of interesting properties including interesting temperature and 3 He concentration dependence. A number of questions concerning the characteristics and origin of this flow remain. Recent results from the Massachusetts group will be presented.

47