Surface Superfluidity in DiluteHe4-He3Mixtures

Quantitative measurements have been made of the superfluid mass per unit area for the interfacial superfluid phase present at the boundary wall of low-concentration mixtures of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. We find a rapid jump in the superfluid mass at the transition temperature in agreement with the prediction of the Kosterlitz-Thouless theory of the superfluid transition in a two-dimensional system.