It also makes theoretical calculations much more difficult, increasingthe need for experimental measurements against which the theories can be compared. For example,early measurements of liquid 3He by Sokol and collaborators showed significant discrepancies withtheoretical calculations. Recent measurements of the density dependence ofthe momentum distribution may help to resolve these discrepancies. Recent work has centered on liquid 3He-4He mixtures, where the interplay between Boseand Fermi statistics dominates the behavior. Measurements by Sokol s group have indicated that the condensate fraction more than doubles in dilute mixtures.
Current theories predict aenhancement of the condensate, but much smaller than the observed results.
In addition, the kinetic energy of the atoms in the mixture, which is ameasure of their localization, does not agree with current theoretical predictions. Much work in this areais required to explore the discrepancies between theory and experiment. Sokol has recently begun studies of the collectiveexcitations of liquid 4He confined in porousglasses. The effects of geometrical confinement on the macroscopic properties hasbeen well studied. The confinement of the superfluid in porous glasses canprofoundly affect its behavior, even to the extent of changing the criticalexponents.