  It is generally believed that when Cooper pairing occurs between two
different species of fermions, their Fermi surfaces become locked together so
that the resultant state remains 'neutral', with equal number densities of the
two species, even when subjected to a chemical potential that couples to the
difference in number densities. This belief is based on mean-field calculations
in models with a zero-range interaction, where the anomalous self-energy is
independent of energy and momentum. Following up on an early report of a
deviation from neutrality in a Dyson-Schwinger calculation of
color-flavor-locked quark matter, we investigate the neutrality of a
two-species condensate using a Yukawa model which has a finite-range
interaction. In a mean field calculation we obtain the full energy-momentum
dependence of the self energy and find that the energy dependence leads to a
population imbalance in the Cooper-paired phase when it is stressed by a
species-dependent chemical potential. This gives some support to the suggestion
that the color-flavor-locked phase of quark matter might not be an insulator.
