SUPERFLUID DROPLETS ON A SOLID-SURFACE

Photographs are presented of isolated superfluid helium-4 droplets pre pared on a cesium surface, the only material known that is not wetted by superfluid helium. Although thermodynamic measurements show that th e cesium surface is highly uniform, the contact angle of the droplets is extremely hysteretic and depends on whether the contact line is adv ancing or receding. Superfluid helium-4 droplets on an inclined surfac e do not flow downhill but rather are strongly pinned to the surface.