Dynamics of the BCC-HCP transition of solid He-4

We are optically studying the phase transition from BCC to HCP of solid He- 4 (1.43 K) at melting pressure to investigate how the crystal changes its s tructure when it is in equilibrium with superfluid. When the temperature wa s changed slowly through the transition, new phase seeds were nucleated som ewhere and those seeds grew in the superfluid phase. The interesting point is that growth of the new seeds is more favorable than the direct solid-sol id Martensitic transition. Whereas at the transition of 1.78 K where the so lid is in equilibrium with the normal fluid, the transition occurred as an ordinary Martensitic transition. (C) 2000 Elsevier Science B.V. All rights reserved.