SUPERFLUID FLOW AND KAPITZA RESISTANCE OF VERY THIN HE-4 FILMS

The thermal-counterflow experiments in the film-vapour system is used to investigate the superflow of very thin He-4 films at temperatures b etween 1.0 K and 2.1 K. We measure the filmflow resistance on both sid es of the Kosterlitz-Thouless 2-D phase transition. On the superfluid side we observe the predicted (AHNS) powerlaw behaviour over a range o f 3 decades in tile flow resistance, the exponent being 2 at the KT-po int and rising with increasing film thickness. On the non-superfluid s ide the powerlaw still rather well describes the massflux dependence o f the flow resistance, the exponent being smaller than 2. The influenc e of the substrate material is studied by comparing the weak binding s olids H-2 and Ne with glass. The second phase transition on H-2, repor ted by Mochel et. al., is not observed. Secondly we check our previous observation of a gradual increase of the Kapitza resistance with decr easing film thickness in a new device with a well-localized heat excha nger.