Figure 6: Crystal flow
Sebastien Balibar and co-workers filled two communicating vessels to a different
height with solid helium-4 (left) and used a camera to see if the two systems reached equilibrium
(i.e. as a liquid would). For crystals with grain boundaries (shown on the right in a solid helium-4
crystal that is about 1 cm square), the team did indeed observe such mass flow.
Source: R Ishiguro, S Sasaki, S Balibar