Surface tension and surface entropy of superfluid He4

We present measurements of the surface tension σ(T) and surface entropy-dσdT of superfluid helium in the temperature range from 0.3 to 2.1 K. The data were obtained by a method in which changes in the capillary rise of the liquid in a parallel plate capacitor are balanced by an electric field which keeps the meniscus stationary. The method is capable of high precision since it does not suffer from many of the errors introduced by imperfections in the capacitor plates. The data show that, even at the lowest temperatures, there are systematic deviations from the Atkins theory of the temperature dependence of σ, although the theory appears to be correct in the limit that the temperature goes to zero. A new version of the theory, which includes the effects of compressibility and the curvature dependence of the surface tension, is in much better agreement with the data for temperature up to ∼ 1 K.