Stability Criteria for Breached Pair Superfluidity
  We present simple, concrete, two-fermion models that exhibit thermodynamically stable isotropic translationally-invariant gapless superfluid states (breached pair superfluidity). The mass ratio between the components and the momentum structure of the interaction are crucial for determining the stability of such states: Idealized, momentum-independent (``contact'') interactions are insufficient. 
Michael McNeil Forbes, Elena Gubankova, W. Vincent Liu, Frank Wilczek