Pair correlation and pair collectivity in neutron-rich nuclei

We describe the neutron Cooper pair, the pair vibrational states and the associated two-neutron transfer strength by applying the Skyrme-Hartree-Fock-Bogoliubov mean-field model and the quasiparticle random phase approximation to neutron-rich Sn isotopes. The wave function of the Cooper pair exhibits a strong spatial correlation favoring short relative distances smaller than a few fm, in contrast to the case of the single-j Cooper pair. The model also predicts an anomalous pair vibration in neutron-rich isotopes beyond the N = 82 magic number, which originates from the weak binding of the last neutrons.