Vortices in Metastable 4He Films

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Liquid helium wets almost all surfaces. This behaviour results from its small dielectric permittivity, e = 1.057, which leads to attractive forces between the helium atoms weaker than those between helium and other atoms [1]. In 1991 Cheng et al., however, predicted that 4He does not wet certain alkali metals. Instead, for some of these metallic substrates, a first-order wetting transition was foreseen [2]. In the alkali metals, weakly bound outer electrons cause a shortrange repulsion for the helium atoms. The resulting temperature-dependent balance between repulsive short-range and attractive long-range forces is at the origin of the wetting phenomenon in liquid helium.