Localization of pairing correlations in nuclei within relativistic mean field models

We analyze the localization properties of two-body correlations induced by pairing in the framework of relativistic mean field (RMF) models. The spatial properties of two-body correlations are studied for the pairing tensor in coordinate space and for the Cooper pair wave function. The calculations are performed both with relativistic Hartree-Bogoliubov (RHB) and RMF projected-BCS (PBCS) models and taking as examples the nuclei Ni-66, Sn-124, and Pb-200. It is shown that the coherence length has the same pattern as in previous nonrelativistic HFB calculations, i.e., it is maximum in the interior of the nucleus and drops to a minimum in the surface region. In the framework of RMF+PBCS we have also analyzed, for the particular case of Sn-120, the dependence of the coherence length on the intensity of the pairing force. This analysis shows that (a) pairing is reducing the coherent length by about 25-30% compared to the RMF limit and (b) after the onset of pairing correlations, the coherent length depends only weakly on the strength of the pairing force.