DYNAMICS AND PARTICLE-HOLE INTERACTIONS IN LIQUID-HE-3 - A GREENS-FUNCTION APPROACH

The dynamics of normal and fully spin-polarized He-3 are studied for momentum transfers below 2 angstrom-1. This study is based on a first-principles calculation of the dynamic susceptibility, chi(Q, omega). We invoke the Baym and Kadanoff (BK) procedure for generating an approximate particle-hole irreducible interaction, I(ph), which is needed in the calculation of chi(Q, omega). The BK procedure yields an I(ph) that conserves particle number, energy, and momentum. When the BK procedure is applied to the Galitskii-Feynman-Hartree-Fock (GFHF) self-energy, the resulting I(ph) consists of direct and induced terms. Previous calculations using GFHF theory have neglected induced effects. For Q < 2 angstrom-1, the induced term contributes significantly to the strength of I(ph). Landau parameters calculated with induced effects included are greatly improved. We compare our (static) I(ph) to those obtained from other first-principles calculations, from polarization-potential theories, and from the available experimental data. In spin-polarized He-3, we find that I(ph) is strongly density dependent. In normal He-3, the same behavior is observed for the spin-symmetric contribution. In contrast, the spin-antisymmetric contribution is nearly independent of density. This finding is in agreement with experiment. For both systems a well-defined zero-sound mode was determined. Using our microscopically determined I(ph), effective mass, Landau parameter F1s, and a polarization-potential form for the frequency dependence of I(ph), we obtained a zero-sound dispersion that agrees well at low Q with the experimentally determined one. Finally, we comment on the relevance of the spin-fluctuation contribution observed in our I(ph) for the case of normal He-3.