Liquid-SolidHe4Interfacial Tension: Temperature Variation near the Superfluid Transition

Accurate measurements of the interfacial tension between solid and superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ show for the first time that it decreases between 1.2 and 1.76 K. The magnitude of this effect is compared with various recent theoretical predictions. A significant contribution is found to come from the entropy of Rayleigh waves. We also discuss the effect of the progressive disappearance of the condensate along the melting curve, near the $\lambda$ transition.