Shadow density matrix for superfluid 4He and the static structure factor

The shadow wave function for the excited states of superfluid 4He is used to construct the density matrix of the system within the independent excitation picture. From the temperature dependence of the total and of the kinetic energy we infer that most of the energy of a roton is kinetic and that a roton lowers the potential energy. From the density matrix we compute the static structure factor S(k;T) and find that thermally excited rotons lead to an increased local order in good agreement with experiment. (orig.)