Third Sound Resonance Studies of HELIUM-3 - Helium -4 Mixture Films.

Third sound velocity and dissipation measurements were performed on 3He-4He mixture films of 3.6 and 5.3 layers 4He and up to 3 added layers 3He in the temperature range 0.05 K T 0.3 K using third sound resonance techniques. The 3He concentration dependence of the velocity was in excellent agreement with a simple layered-film model down to the lowest concentrations studied. At the higher 3He concentrations the velocity began to deviate from the model, rising above it. The concentration dependence of the dissipation showed some unique structure with a maximum at 0.3-0.5 layers added 3He for both 4He coverages. The third sound velocity in the low concentration mixture films had very little temperature dependence in the range studied. The dissipation, however, had some definite temperature dependent structure which evolved with concentration. This evolution was most pronounced at concentrations near the dissipation maximum and eventually became exponential at the higher coverages. Fitting these exponentials produced estimates of the difference in binding energy for the 3He states in and on the film. In this higher 3He concentration regime, a temperature dependence of the velocity was observed which began as a small peak at about 0.15 K and eventually became a step at the highest concentrations studied. The exponential nature of the dissipation became clouded when the velocity evolved into this last behavior.