Momentum distribution and excitation spectrum of liquid helium

Abstract

The consistency of recent experimental and theoretical analyses of liquid He⁴ is investigated. Further evidence is found for a strong depletion of the zero momentum state. The modifications of a Brueckner-Sawada type approximation implied by this depletion as well as by the existence of a net attraction of the helium atoms are discussed. It is found that a single particle model which does not allow for a sufficient width in the single particle spectral function is incapable of giving the observed excitation spectrum as well as the binding energy of liquid He. Better results are obtained with a single particle model which usesFeynman's energiesk ²/2ms(k) instead of the peak energy in neutron scattering.