The λ-Phenomenon of Liquid Helium and the Bose-Einstein Degeneracy

IN a recent paper¹ Fröhlich has tried to interpret the λ-phenomenon of liquid helium as an order–disorder transition between n holes and n helium atoms in a body-centred cubic lattice of 2n places. He remarks that a body-centred cubic lattice may be considered as consisting of two shifted diamond lattices, and he assumes that below the λ-point the helium atoms prefer the places of one of the two diamond lattices. The transition is treated on the lines of the Bragg-Williams-Bethe theory as a phase transition of second order in close analogy to the transition observed with Î-brass. Jones and Allen in a recent communication to NATURE² also referred to this idea. In both these papers, use is made of the fact, established by the present author, that with the absorbed abnormally great molecular volume of liquid helium (caused by the zero motion³) the diamond-configuration has the lowest potential energy among all regular lattice structures⁴.