Equation of State for Hard-Core Quantum Lattice System
It is well known that the melting curves for 3He and 4He have a negative slope for a while until a minimum melting temperature is reached, and increase at higher temperatures.1 For 3He the negative slope is explained by taking into account a large entropy of spin disorder in solid phase and a small entropy in the ordered Fermi fluid. For 4He the entropy from phonon excitations plays an important role in accounting for this phenomenon.
KeywordsNegative Slope Classical Lattice Model Pair Approximation Cluster Variation Method Phonon Excitation
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- 1.J. Wilks, The Properties of Liquid and Solid Helium, Oxford University Press (1967).Google Scholar