Systematic studies of the influence of single-particle resonances on neutron halo and skin in the relativistic-mean-field and complex-momentum-representation methods

The newly developed relativistic-mean-field and complex-momentum-representation (RMF-CMR) method is used to explore the exotic structure for the neutron-rich Ca, Ni, Sn, and Pb isotopes. The results are compared with the relativistic Hartree-Bogoliubov (RHB) calculations as well as the available data. The calculated root mean square (rms) radius of the neutron and proton suggests a halo or giant halo structure in the Ca isotopes with neutron number more than N = 40, and a thick neutron skin in the extremely neutron-rich Ni, Sn, and Pb isotopes. The extracted two-neutron separation energies agree the experimental data as well as the RHB calculations. The conclusions are supported by the available single particle levels, the valence nucleon occupations, the contributions of resonant and weakly bound levels to the neutron rms radius, the density distributions of the occupation levels, and the total neutron, proton, and matter densities. Especially, it is found that the unusually increasing radius comes mainly from the contributions of the weakly bound levels with lower orbital angular momentum, and the diffuse density distributions, like the halo, originate mostly from the resonant levels with lower orbital angular momentum in the vicinity of the continuum threshold. The predication on the structure of halo and skin in the neutron-rich Ca, Ni, Sn, and Pb isotopes are of referential value for experiment.