Proximity effect at a He II–He I interface under microgravity

The proximity effect is responsible for the existence of a transition region with graded variation of the superfluid component density instead of a sharp boundary at the level where the hydrostatic pressure induces a He II–He I phase transition. Under microgravity the characteristic length of this effect increases and the conditions become more conducive for performing measurements in the transition region. The problem of expanding the thermodynamic potential in a power series near a He II–He I interface is considered. The critical size of the superfluid region is determined.