Torsional Oscillator (TO) experiments done on solid 4He show a partial mass decoupling. First reported by Kim and Chan (1), and later confirmed by many others, these results are under a debate regarding their interpretation as a sign of supersolidity. We performed TO measurements on single crystals of 4He at temperatures between 1.1K and 1.9K, and observed large mass decoupling associated with the generation of disorder. We repeated the experiment, changing the crystals’ growth direction with respect to the TO’s rotation axis. We found a significant difference in mass decoupling when the growth direction was perpendicular to the rotation axis, for the different crystal symmetries. Dislocation dynamics in a solid could offer one possible explanation of this anisotropy. However, the dissipationless nature of the mass flow remains a puzzle.

[1] E. Kim and M. H. Chan, Science, 305, 1941 (2004)