On the structure of the paired states

Abstract

In this paper the quasi-particle structure of the ground state of the pairing Hamiltonian is analysed for the Ni isotopes and 206Pb. The particle-number projected Bardeen-Cooper-Schrieffer states are used for describing the states under consideration. The quasi-particle amplitudes are evaluated in the saddle-point approximation. The amplitudes with the number of quasi-particles a multiple of four are shown to be comparable with the quasi-particle vacuum amplitude. The value of the other quasi-particle amplitudes depends essentially on the system considered. In particular, the two-quasi-particle component can sometimes be comparable with the four-quasi-particle one (206Pb). On the basis of the data obtained it is concluded that the random phase approximation ground-state wave function with small admixture of the quasi-particle components, the components with the odd number of quasi-particle pairs being neglected completely, is rather poor.