INTERPLAY OF SUPERFLUIDITY AND PHASE-SEPARATION IN ADSORBED FILMS

We note that when the line of superfluid transitions intersects a line of phase separation near the critical point of the latter, one should expect the simultaneous occurrence of both high- and low-density superfluids. The signals from a third-sound experiment depend distinctively upon the density, there being seven different regions of characteristic response, which facilitates the identification of such a possibility. This scenario may provide an explanation for recent observations on helium adsorbed on hydrogen, in which case the critical point would be that of a layer transition. We also describe the interesting progression which would be observed in the temperature-chemical potential plane as the superfluid line approaches such a point. This progression might be observable in microbalance experiments on the approach of the superfluid transition to the prewetting critical point.