Coherence features of the spin-aligned neutron-proton pair coupling scheme

The seniority scheme has been shown to be extremely useful for the classification of nuclear states in semi-magic nuclei. The neutron-proton (np) correlation breaks the seniority symmetry in a major way. As a result, the corresponding wave function is a mixture of many components with different seniority quantum numbers. In this paper, we show that the np interaction may favor a new kind of coupling in N=Z nuclei, i.e. the so-called isoscalar spin-aligned np pair mode. Shell model calculations reveal that the ground and low-lying yrast states of the N=Z nuclei 92Pd and 96Cd may be mainly built upon such spin-aligned np pairs, each carrying the maximum angular momentum J=9 allowed by the shell 0 g9/2 which is dominant in this nuclear region.