Density-density response of dilute−43He mixtures at low temperatures

An attempt is made to describe the dynamical structure factors of $^{3}\mathrm{\ensuremath{-}}^{4}$He mixtures recently measured by F\aa{}k et al. [Phys. Rev. B 41, 8732 (1990)] in the polarization potential approach, which is formulated to include the structure factor ${\mathit{S}}_{34}$. Good qualitative agreement of calculation and data is achieved. It turns out that virtual phonon-roton excitations provide significant strength to the particle-hole peak of the structure function and that virtual quasiparticle-quasihole excitations contribute significantly to the phonon-roton peak.