Thermodynamics of the Surface of [sup.4]He Crystals

The conditions for applicability of the mean field theory for describing the thermodynamics of the surface of 4He crystals are investigated based on analysis of experimental data. It is found that although the faceting phase transition itself is a Berezinsky-Kosterlitz-Thouless phase transition, the thermodynamic potential outside a narrow neighborhood of the transition temperature can be expanded into a series in terms of the Landau theory of second-order phase transitions.