Competition between the superfluidity and the slippage of ⁴He films adsorbed on porous gold

We have carried out QCM measurements for ⁴He films adsorbed on porous gold in the crossover region between the superfluidity and slippage. In relative low areal densities, the resonance frequency increases gradually below T_S due to the slippage of solid film, while the superfluid onset is observed in high areal densities. In the crossover region, we observed a peuliar behavior: The inrease in the resonance frequency below T_S is suddenly suppressed at a certain temperatue T_D. From these observations, it is oncluded that the superfluidity and the slippage of ⁴He competes with eah other.