Pairing correlations in atomic nuclei have shown to play a crucial role to many properties, in spite of the small effect on the total binding energy. The talk will start with introductory remarks on the symmetry energy in atomic nuclei, giving a different interpretation fro m what is found in standard text books. It will then move on to the specific properties of N=Z nuclei, where neutron and proton occupy near degenerate orbitals.
This specific situation enables two different kind of Cooper pairs to be formed, that either have iso spin T=0 and intrinsic spin S=1 or T=1 and S=0. It isshown that both condensates can coexist and generate a wave function that is a coherent superposition of both coupling modes. The effect of iso spin excitation is then studied and its effect on the pair correlations. A Meissner effectin iso spin is the resulting from those excitations. The formalism of approximate projection and symmetry restoration is discussed.
