Low-friction state of 4He films adsorbed on grafoil Original Research Article

The interfacial friction of 4He films adsorbed on Grafoil was measured using the quartz-crystal microbalance (QCM) technique. The frictional force shows a nonlinear behaviour in the oscillating amplitude, and decreases relatively with increasing amplitude. In addition, it was found that this force decreases below a certain temperature TS, i.e., the film sets in a low-friction state below TS. At a large amplitude, the frictional force of the low-friction state is much smaller than that of a small amplitude, and this state remains metastable concerning the change in the oscillating amplitude.