Specific heat and phonon dispersion of liquidHe4

Abstract

The specific heat of liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ was measured with high precision in the temperature range from 65 to 850 mK and at sixteen molar volumes corresponding to the pressure range from vapor pressure to 25 bars. Several different analyses performed on these data yield quantitative information concerning the magnitude of the anomalous phonon dispersion as a function of pressure. The findings are generally in good agreement with the results indirectly derived from sound-propagation measurements. The specific heat data also provide precise values of the roton parameters as a function of pressure. There is an unexplained discrepancy between these values and those resulting from neutron scattering measurements.