Isoscalar-isovector proton-neutron pairing and quartet condensation in N = Z nuclei

We show that the correlations generated in the ground state of N = Z nuclei by the isovector and isoscalar pairing forces can be treated with high precision as a condensate of alpha-like quartets. To treat these correlations, the quartet condensation model (QCM) is extended to the treatment of spherically symmetric isovector (T = 1, J = 0) and isoscalar (T = 0, J = 1) pairing forces. Within the QCM, we discuss the competition between T = 1 and T = 0 pairing correlations in the case of a two-level model and for N = Z nuclei with nucleons moving in the open shells above O-16, Ca-40, and Sn-100. We show that, in N = Z systems, isovector and isoscalar proton-neutron pairing correlations always coexist.