Pair Correlation and Collective Excitations:. Continuum Qrpa Approach to Exotic Nuclei Near Drip-Line

By using the continuum quasiparticle random phase approximation, which we recently formulated on the basis of the coordinate-space Hartree-Fock-Bogoliubov theory, we investigate pairing effects on the low-lying dipole strength in neutron rich oxygen isotopes near the drip-line. The neutron pairing enhances the dipole strength near the threshold, especially in the case of the surface pairing. Analysis shows that spatially correlated spin-singlet neutron pairs (di-neutrons) are formed in the external region, and the low-lying dipole strength is characterized by motion of the correlated neutron pairs against the core.