Heat transport via evaporation of superfluid helium films: Giant effective Kapitza resistance

We report measurements of heat transport from a solid substrate into a thick superfluid 4He film at sub-kelvin temperatures. We believe this transport is bottlenecked by the insufficient generation of excitations in the film capable of causing evaporation of atoms. An effective film temperature and an effective Kapitza resistance are defined. The effective Kapitza resistance is more than 3 orders of magnitude larger than for bulk helium, with an exponential temperature dependence