Two dimensional phase separation and spectroscopy of 3He in 4He films

The behavior of two dimensional 3He realized as a layer at the surface of thin superfluid films has been studied with measurements of heat capacity. It is found that for the 10.0 A and 12.3 A thick 4He films, and starting at a 3He coverage of 0.058 layer, 3.7 x 10-14 A-2, the data show a very sudden onset of degeneracy below about 10 mK. It is found that these data are consistent with phase separation in the two dimensional layer of 3He at the surface of the 4He film. The data suggest that below the phase separation temperature the 3He consists of a very dilute phase, in equilibrium with a concentrated phase. Above the phase separation temperature 3He becomes homogeneously spread over the 4He film. This represents the first observation of phase separation for two dimensional 3He. At higher temperatures the 3He is promoted from its ground state to excited states. For thin films of 4He the first excited state, where the 3He is still bound to the 4He film, is also two dimensional in character. States farther above this represent evaporation of the 3He into the vacuum above the film. With this picture of the spectrum one can calculate the heat capacity which is parametrized by the energy difference between the excited state and the ground state and the effective masses of the 3He