Critical fluctuation-induced thinning of 4He films near the superfluid transition

We report dielectric constant measurements showing critical fluctuation-induced thinning of He-4 films near the superfluid transition. The films are adsorbed on a stack of copper electrodes suspended at different heights above bulk liquid. We calibrate the measurements by assuming that the film thickness away from the transition region at different heights is accurately given by theory. The thinning is found to be consistent with finite-size scaling, if the value of the scaling function for each thickness is normalized by its value at the minimum.