Attractive and repulsive contributions of medium fluctuations to nuclear   superfluidity
  Oscillations of mainly surface character (S=0 modes) give rise, in atomic nuclei, to an attractive (induced) pairing interaction, while spin (S=1) modes of mainly volume character generate a repulsive interaction, the net effect being an attraction which accounts for a sizeable fraction of the experimental pairing gap. Suppressing the particle-vibration coupling mediated by the proton degrees of freedom, i.e., mimicking neutron matter, the total surface plus spin-induced pairing interaction becomes repulsive. 
G.Gori, F. Ramponi, F. Barranco, P.F. Bortignon, R.A. Broglia, G.   Colo', E. Vigezzi