Theory of the temperature dependence of spatial correlations in liquid 4He

The temperature dependence of the structure factor S(k,T) of liquid 4He is studied on the basis of a model density matrix based on the elementary excitation picture and with roton excitations described in terms of the Feynman wave function. S(k,T) is constructed starting from the experimental low-temperature S(k), the energy spectrum epsilon/sub k/(T), and the linewidth delta/sub k/(T). No assumption is needed on the form of the Hamiltonian. The main peak of S(k,T) has an anomalous behavior, it increases its height and becomes sharper as the temperature is increased; this is due to thermal population of roton states that causes an enhancement of the short-range order. This anomalous behavior ends slightly above T/sub lambda/ when rotons become overdamped. Our result is in good quantitative agreement with experiment. This temperature effect becomes stronger at high density