Early stages of spinodal decomposition in superfluidHe3-He4mixtures

A generalization of the linearized analysis of Cahn, Hilliard, and Cook is applied to a simple model of phase separation dynamics in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mixtures at early times. An instability region is found in which the structure function for concentration fluctuations exhibits maximum growth at a nonzero wave vector. The coupling of concentration fluctuations to the superfluid second-sound mode produces an additional "flickering" component in the scattering. Equilibrium experimental data from both sides of the coexistence curve are used to estimate the size of these effects. The instability region is found to be quite asymmetrically placed inside the two-phase region.