CRYSTALLINE SURFACES IN HELIUM

The particular properties of helium at low temperature recently allowed important progress in the general understanding of the structure and dynamics of crystal surfaces. Excellent agreement has been found between experimental results in helium 4 and the renormalization group theories of the roughening transition, which predict that it is an infinite order (Kosterlitz-Thouless) phase transition. The dynamic roughening of a crystal surface, i.e. the influence of a finite growth rate, has been particularly clarified. The dominant growth process of smooth faces close to their roughening transition has been shown to be the two-dimensional nucleation of terraces. In both helium 3 and helium 4, it also appeared possible to measure and analyze the three interface coefficients which describe the dissipation at rough crystal surfaces is non-equilibrium situations. The latter studies provide interesting information on the elementary processes (heat and mass flow) which occur in quantum liquids during their crystallization. A general review of all these phenomena is given. © 1990.