REFINEMENT OF THE DYNAMIC THEORY OF SUPERFLUID-HELIUM FILMS

The standard theory of the dynamics of superfluid films, although in g ood qualitative agreement with experiment, is not in perfect quantitat ive agreement. Until now it has not been clear whether the disagreemen t is due to inaccuracies in the theory oi because the experiments invo lve an extra physical effect not included in the theoretical model. He re we show how the theory can be refined: the ambiguity that arises ov er the difference between free and bound vortices in the superfluid sy stem is avoided by using an ansatz in which all vortices are considere d paired the interaction between vortices is calculated using recently developed versions of the Kosterlitz recursion relations accurate to higher older in the fugacity; the linear response is calculated using accurate numerical techniques. We present a detailed comparison of the mortified theory's predictions I vith recent experimental results. We Sind that, despite the changes in the theory, the agreement, with exp eriment remains only qualitative, suggesting that the theory fails to capture some of the essential physics of experiments on Helium films.