Prewetting phase diagram ofHe4on cesium

We have studied the adsorption of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ on cesium in the temperature range from 1.3 to 4.1 K. The ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ film undergoes a first-order phase transition known as prewetting. The prewetting line intersects the coexistence curve at the wetting temperature, ${\mathit{T}}_{\mathit{w}}$=1.95 K, and terminates at ${\mathit{T}}_{\mathit{c}}$=2.5 K, the prewetting critical point. There are dramatic hysteresis effects when the temperature of the system is varied at coexistence in the vicinity of ${\mathit{T}}_{\mathit{w}}$. This is the first experimental realization of a complete prewetting phase diagram.