Quasiparticle interactions in two-dimensional 3He on 4He films

Measurements are reported of the heat capacity of He-3 bound to an atomically layered He-4 film on the surface of graphite. At He-3 coverages n(3) < 4 nm(-2), the He-3 forms a uniform 2D Fermi system. Thereafter with increasing n(3) we resolve two steps in the heat capacity, each arising from the formation of a further 2D continuum built on excited surface-normal states. We infer information on the hydrodynamic mass, quasiparticle interactions, and energetics of these states. Both short range repulsive interactions and ripplon mediated quasiparticle interactions are important.