Theory of SolidHe4

Using a phenomenological approach, it is shown first that solid ${\mathrm{He}}^4$ in equilibrium with liquid ${\mathrm{He}}^4$ II along the phase separation line, as well as at pressures somewhat above the melting pressure, should have anomalous thermal properties over a finite temperature range or, at least, at isolated temperatures. Such a behavior of the solid results from a correlation of thermodynamic character of its thermal properties with those of the anomalous liquid. The predicted anomalies of the solid will then be effectively verified in terms of rigorous thermodynamics and somewhat incomplete data available on liquid and solid ${\mathrm{He}}^4$ along the melting line over a finite temperature interval. A specific anomaly of the melting pressure consisting in a shallow temperature minimum will be predicted at low temperatures, where both the liquid and solid phases are assumed to exhibit normal static thermal properties. The persistence of the anomalous equilibrium properties of liquid ${\mathrm{He}}^4$ II on solidification will be discussed qualitatively as suggesting a similar origin of these anomalies in both phases, such a situation having been shown previously to exist with respect to the thermal anomalies of liquid and solid ${\mathrm{He}}^3$.