Superfluidity in asymmetric nuclear matter

The onset of superfluidity in isospin-asymmetric nuclear matter is investigated within the BCS theory. A neutron-proton superfluid state in the channel S-3(1)-D-3(1) comes about from the interplay between thermal excitations and separation delta mu of the two Fermi surfaces. The superfluid state disappears above the threshold value of the density-asymmetry parameter alpha=(n(n)-n(p))/n similar or equal to 0.35. For large enough shift between the two Fermi surfaces delta mu=1/2(mu(n)-mu(p)) the transition to the normal state becomes a first-order transition and a second gap solution develops. This solution, however, corresponds to a metastable superfluid state which is unstable with respect to the transition to the normal state.