We present a complete set of data describing the nucleation both of superfluidity and phase separation at container walls in liquid 3He-aHe mixtures. The appearance of superfluidity and the growth of phase-separated films are measured locally at the walls. A theoretical interpretation is given, important results of which are that the phase separation and superfluid transitions become uncoupled when the transitions are localized near the walls and that quantum fluctuations most probably strongly affect the nature of the superfluid nucleation transition at low temperature. Further, comparison of our results with data for transitions in pure 4He films demonstrates that a universality principle governs the transitions in both systems.
Third-sound velocity measurements in He-He mixture films are used to obtain the phase diagram for different coverages. The characterization of these films is discussed, and a correct parameters choice is proposed. Using a rough estimate of the superfluid density, we find that at the superfluid transition temperature the same universal feature as in 4He film is observed. The general behavior of our films is, ho~ever, not similar to theoretical predictions for two-dimensional mixtures, and the phase separation is not detected. New experiments are suggested by our results in order to clarify the behavior of mixture films.
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