PHASE-SEPARATION OF LIQUID HE-3-HE-4 MIXTURES - EFFECT OF CONFINEMENT

We study the phase separation of helium mixtures inside thin channels in contact with a bulk He3 bath at zero temperature. It is found that the substrate potential favors mixing near the walls. While in bulk, the transition takes place between a He4-rich mixture with 6.6% of He3 and pure He3; in thin channels, the He4-rich phase is richer in He3 and the He3-rich phase contains a nonzero fraction of He4. We anticipate that both phases can be superfluid, so that the superfluid line is detached from the coexistence region. The behavior of helium mixtures in porous aerogel is discussed in relation to the present findings. © 1995 The American Physical Society.