Novel wetting behavior in quantum films

Theory and experiment have revealed that novel behavior occurs when a Cs surface is exposed to He4 vapor. For temperature T below the wetting temperature (Twf2 K), He4 forms only a microscopically thin film as the vapor pressure P increases from zero to its saturated value. For intermediate values of T (TwTTcf2.5 K), the film thickness jumps discontinuously at a prewetting transition pressure Ppw(T). For P>Ppw, and for all P if T>Tc, the film grows continuously to infinite thickness as saturation is approached. Microscopic theories of these phenomena are discussed in terms of the basic physics of electrons and atomic interactions. Initial experimental observations are summarized. Related phenomena of interest are described, including observation of prewetting with adsorbates other than He and substrates other than Cs.