On the Growth Dynamics of 4He Crystals near the First Roughening Transition

The first roughening transition of a surface of hcp 4He crystals was carefully studied in Paris in 1980s. By investigating the growth dynamics of the (0001) facet, the free energy of an elementary step was measured in the close vicinity of the transition and a good agreement was found with the theory of critical fluctuations developed by Nozieres and Gallet. We believe, however, that the interpretation of the growth data near the roughening transition made by the Paris group is not self-consistent. We argue that with the step energies they obtained, assuming that the growth is due to the process of 2D-nucleation of terraces, another growth mechanism provided by screw dislocations should be much more effective.