Thermodynamic properties of condensed interacting bosons and properties of liquid 4He below lambda transition

Liquid 4He, below its lambda transition, is found to exhibit a phase change around 0.6 K, and the recent theoretical studies on the interacting bosons with a two-body potential composed of a hard core followed by two Gaussians have indicated an energy excitation spectrum similar to that of liquid 4He. Following this information from experiment and theory, the thermodynamic function [P/(rhokT)-1]=F(T,V) (where P is the pressure, rho the particle number density, k the Boltzmann constant and T the temperature) has been calculated for a system of bosons interacting through a two-body potential composed of a hard core plus two Gaussians following statistical mechanical methods. The results indicate that (1) the existence of Gaussian tails after the hard core drastically alters the physical proterties of the interacting bosons at low temperatures, and(2) the physical properties of such a system undergo rapid changes around 0.8 K just as liquid 4He(He II) is found to have rapid changes around that temperature. (author)