A fermi disks model for the dynamical response of films of liquid He

We develop a model for the dynamical susceptibility of films of liquid He adsorbed on substrates. Although the film cannot be regarded as a two-dimensional system in coordinate space, we show that its spectrum of elementary excitations corresponds to that of a collection of two-dimensional Fermi liquids in momentum space, which might be pairwise coupled through the atom–atom interaction. The model is applied to compute the response of the film to density fluctuations and can be straightforwardly extended to investigate the spin susceptibility