Condensed water in superfluid He-II

It was found that when ⁴He gas containing water vapor as an impurity condenses on the surface of superfluid He-II cooled to ∼ 1.4 K, semitransparent clouds (icebergs) form in the volume of a glass cell filled with He-II below the He-II surface. The form of the icebergs extracted from the superfluid liquid remains virtually unchanged on heating up to ∼ 1.8 K. In the temperature range 1.8–2.2 K the thermometers register sharp temperature jumps, which are accompanied by jumps in the gas pressure in the cell and a repeated decrease, by more than two orders of magnitude, in the total volume of the condensate, i.e., the water content in the volume of an iceberg does not exceed 10²⁰H₂O molecules per 1 cm³. It can be inferred that porous icebergs, permeated with superfluid liquid and containing cores consisting of small clusters surrounded by a layer of solidified helium, form in the volume of He-II as the gas mixture condenses. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 11, 744–748 (10 December 1999)