HELIUM WETTING - THEME AND VARIATIONS ON INHOMOGENEOUS HELIUM

The surprising discovery, in 1991, that liquid helium does not wet a c esium surface at low temperature has triggered an important activity b oth theoretical and experimental : helium has become a model system fo r the study of wetting transitions. After summarizing the main theme o f helium wetting, I will focus on more recent studies, such as the str ucture and excitations of helium interfaces, experiments on the capill ary rise, the ''surfactant effect'' of helium-3 impurities on liquid h elium-4 and the ''quantum prewetting transition'' of pure helium-3. Un expected consequences on the phase separation of He-3-He-4 mixtures in restricted geometry will be drawn.