Phase-separation curve of−43He mixtures under pressure

The solubility of $^{3}\mathrm{He}$ in $^{4}\mathrm{He}$ has been measured under pressure up to 20 bars in the temperature range between 1 and 250 mK. At temperatures below 60 mK, the solubility varies as ${\mathit{T}}^{2}$ at all pressures. The coefficient of the ${\mathit{T}}^{2}$ term at 0 bar, \ensuremath{\beta}, is 8.29\ifmmode\pm\else\textpm\fi{}0.03 ${\mathrm{K}}^{\mathrm{\ensuremath{-}}2}$, lower than the values of 9--11 ${\mathrm{K}}^{\mathrm{\ensuremath{-}}2}$ reported previously. The value of \ensuremath{\beta} rapidly decreases down to 3.92\ifmmode\pm\else\textpm\fi{}0.03 ${\mathrm{K}}^{\mathrm{\ensuremath{-}}2}$ at 15 bars with increasing pressure. The interaction potential between $^{3}\mathrm{He}$ quasiparticles is obtained by analyzing the solubility data on the basis of Ebner's formula. The effective mass derived from the potential has a weak and positive dependence on the $^{3}\mathrm{He}$ concentration at all pressures.