The roughening transition of a growing 4He crystal

We present a careful study of the growth of hexagonal close-packed 4He crystals near the roughening transition of their (0001) surfaces, at ΤR, for a surface state intermediate between smooth and rough. It exists in a temperature domain whose width increases with the applied driving force. All our experimental results are consistent with a new calculation base don the critical theory of roughening, which predicts a completely continuous or infinite-order transition. Precise values are deduced for the roughening temperature (ΤR = 1.28 ± 0.01 Κ) and the relative amplitude of the lattice potential (tc = 0.63 ± 0.13). (12 refs., 6 figs.)