THE GROWTH DYNAMICS OF HELIUM CRYSTALS

A rich variety of phenomena are found when studying the growth of helium crystals. In the present review, a particular emphasis is given on three particular topics. We first compare rough surfaces in helium 4 and in helium 3, and show how very different thermal excitations lead to very different growth processes. We then summarize the results obtained on the roughening transition and insist on the importance of the dynamic roughening in the weak coupling limit, a phenomenon which reasonably explains the observed roughening of helium 3 crystals. This leads us to a third part, where we present a calculation of the angular variation of the surface stiffness of vicinal surfaces on helium 4 crystals. Agreement is found between the theory by Nozieres and Gallet and the various experiments performed in Paris and Moscow. We conclude with a list of questions which call for further studies, namely the effect of step-step interactions, impurities, strains, etc.