Superfluid Fraction of ³He-⁴He Mixtures Confined at 0.0483μm between Silicon Wafers

We report measurements of the superfluid fraction ρ_s/ρ of films of ³He-⁴He mixtures confined between silicon wafers at 0.0483μm separation. The data obtained using adiabatic fountain resonance (AFR) can be used to test for the first time expectations of correlation-length scaling in the case of planar mixtures. For the mixtures, the data for ρ_s/ρ collapse well on a universal function. The dissipation associated with AFR can also be scaled, and indicates two-dimensional crossover. These results are in contrast to pure ⁴He, where over a wider range of confinements, the data for ρ_s/ρ are found not to scale.