T=0 and T=1 pairing and the formation of four-particle correlated structures in the ground states of Z=N nuclei

The T=0 and T=1 pairing correlations are discussed within the framework of two simple models: the SO(8) algebraic model and the single-j model with a surface-delta interaction. The possibility of an approximate description of the ground-state wave functions in terms of correlated four-particle T=0, S=0 (alpha -like) structures is investigated. The overlap of the approximate and the exact wave functions is shown to be larger than 0.93 for any relation between the T=1 and T=0 pairing strengths. The influence of the neutron-proton pairing interaction terms on the quadrupole sum rule and on the ground-state magnetic moments of the odd nuclei with Z=N+/-1 is analyzed.