Model for the extreme wetting hysteresis of liquid helium on cesium

Although the liquid-He-4-cesium system is a nearly ideal one for studying w etting phenomena, it can show extreme hysteresis which is profoundly nonide al in behavior. It is suggested that this is due to the roughness of these Cs surfaces. We show that stable micropuddles of liquid He-4 can form in sh allow cavities on a Cs surface. It is the potential to form micropuddles, a s the liquid tries to recede, which pins the contact line due to the large energy needed to create the surface of a micropuddle. This model also accou nts for the memory that these surfaces have of being in contact with liquid He-4.