Molar volume of superfluid3He−4Hemixtures: The dependence of the Bardeen-Baym-Pines parameter on temperature, pressure, and3Heconcentration

Abstract

We have developed a new method for determining the Bardeen-Baym-Pines (BBP) parameter of a superfluid ${}^3\mathrm{He}{-}^4\mathrm{He}$ mixture from the measurement of its molar volume within the wide ranges of temperature, pressure, and the ${}^3\mathrm{He}$ concentration. The method and the results are described. The ranges of the present investigation are 0.4–660 mK in temperature, 0.3–10 ${\mathrm{k}\mathrm{g}\mathrm{f}/\mathrm{c}\mathrm{m}}^2$ in pressure, and 0.07–0.39 in the ${}^3\mathrm{He}$ concentration. The data obtained are fitted with a formula based on the phenomenological theory of dilute solutions of ${}^3\mathrm{He}$ in superfluid ${}^4\mathrm{He}.$ Our empirical formula can reproduce the experimental values of the BBP parameter within the accuracy of 1%. The argument on the absolute uncertainty is also given.