Surface tension of liquid 4He and 3He

Abstract

Surface tensions of liquid 4He and 3He have been measured down to 0.3 K by using the surface-wave resonance method. Measurements with 3He have been made further, down to 20 mK, by the capillary-rise method. Liquid 4He shows a T7/3 temperature dependence up to approximately 1 K, indicating that the ripplon excitation is the predominant contributor in this temperature range. It is concluded with the superfluid 4He that the "surface energy" of the Bose–Einstein condensate (BEC) gives a major contribution to the surface tension, from which we have deduced n0, the fraction of BEC. Liquid 3He shows a T2 temperature dependence from 0.3 K to about 1 K. The result is attributed to both the effect of 3He quasi particles, which hit the surface, and the ripplon. The latter has never been seriously thought to exist on the 3He surface.An unexpected behavior of the 3He surface tension has been found below approximately 200 mK. The surface tension does not obey the T2 temperature dependence but deviates downward around 200 mK.Surface tensions of 4He and 3He have been measured also in the vicinities of liquid–vapor critical points.