  We discuss the dynamics of phase separation through the process of spinodal
decomposition in a Fermi superfluid with population imbalance. We discuss this
instability first in terms of a phenomenological Landau theory. Working within
the mean-field description at zero temperature, we then find the spinodal
region in the phase diagram of polarisation versus interaction strength, and
the spectrum of unstable modes in this region. After a quench, the spinodal
decomposition starts from the Sarma state, which is a minimum of the free
energy with respect to the order parameter at fixed density and polarisation
and a maximum at fixed chemical potentials. The possibility of observing
non-trivial domain structures in current experiments with trapped atomic gases
is discussed.
