EXPERIMENTAL SURVEY OF WETTING AND SUPERFLUID ONSET OF HE-4 ON ALKALI-METAL SURFACES

We present a survey of the wetting behavior of He-4 on evaporated film s of rubidium, potassium and sodium. He-4 wets these surfaces at all t emperatures. Off coexistence on rubidium and potassium there is a prew etting transition that is closely coupled with superfluid onset and po ssibly a surface tricritical point where the prewetting transition and superfluid onset intersect. Sodium has a prewetting critical temperat ure well below 1 K. Wetting and superfluid onset phase diagrams for He -4 on rubidium and potassium are presented and compared with that of H e-4 on cesium.