Heat capacity of atomically layered 3He-4He mixture films

We report preliminary results of the first heat capacity measurements on atomically layered He-3-He-4 mixture films adsorbed on the surface of graphite. The He-4 film consists of two solid and two superfluid atomic layers. The heat capacity has been investigated over the range 1 - 70mK as a function of the surface density of He-3 atoms added to the film. At cover ages n(3) < 4 nm(-2), the He-3 forms a uniform two dimensional Fermi system. The coverage dependence of the linear coefficient of the heat capacity, gamma, allows a determination of the hydrodynamic effective mass and F-1(s). At higher coverages a step-like increase in gamma is observed, interpreted as the formation of a second two dimensional Fermi system.