ABSTRACT
Although the liquid- 4He-cesium system is a nearly ideal one for studying wetting phenomena, it can show extreme hysteresis which is profoundly nonideal in behavior. It is suggested that this is due to the roughness of these Cs surfaces. We show that stable micropuddles of liquid 4He can form in shallow cavities on a Cs surface. It is the potential to form micropuddles, as 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 accounts for the memory that these surfaces have of being in contact with liquid 4He.
ABSTRACT
Experimental evidence is presented that shows that the momentum of a R- roton (a particle-like excitation in liquid helium-4) is antiparallel to its velocity. Although this is anticipated from the negative slope of the dispersion curve for these excitations, it has only been possible to test since the development of a source of ballistic R- rotons. The backward refraction of the quantum evaporation process, which is the signature of antiparallel momentum and velocity, is observed.
