Quartz Oscillator Study of Monolayer ~4He and ~3He-~4He Mixture Films Adsorbed on Solid H_2

摘要

The superfluid transition in submonolayer and monolayer ~4He films and ~3He-~4He mixture films on solid H_2 has been studied using a quartz crystal microbalance technique. Kosterlitz-Thouless (KT) transitions were observed in submonolayer ~4He films with density greater than 0.062±0.002 A~(-2). We determine a binding energy of ~4He to 0.241 A~(-2) H_2 of －15.7K in the presence of≈1 monolayer of ~4He. At several ~4He coverages, a range of submonolayer ~3He coverages was studied (n_3≤0.0567 A~(-2)). With each increase in the ~3He coverage, the KT transition temperature decreased. For the higher coverage mixture films studied (n_4≥0.0726 A~(-2)) we observed an apparent second decoupling of the film from the quartz oscillator frequency in addition to the KT transition. We have studied the coverage dependence of this new feature.