Conclusions

In the present study we presented a model description of the four SD bands in nuclei around ⁶⁰Zn in order to evaluate the role of the T=1 and T=0 pairing correlations at high spin in N$\simeq$Znuclei. On the one hand, we have shown that calculations with no pairing, whether within the Strutinsky-Woods-Saxon or Skyrme-Hartree-Fock approaches, provide an excellent description of all bands except the one in the doubly-magic N=Z nucleus ⁶⁰Zn. On the other hand, the standard Lipkin-Nogami treatment of the T=1 pairing gives a fair description of the bump in the second moment of inertia ${\cal J}^{(2)}$ in ⁶⁰Zn, which results from the simultaneous alignment of the g_9/2 pairs of neutrons and protons, but fails in describing low values of ${\cal J}^{(2)}$ in all the four nuclei at high frequencies. The latter effect results from a gradual disappearance of the T=1 pairing correlations with increasing spin, and cannot be avoided if these same pairing correlations have to be responsible for the positive result in ⁶⁰Zn. We have also shown that the deformation changes caused by polarization effects of high-jorbitals are strong, and strongly modify the simple blocking picture when going from even to odd isotopes. Nevertheless, even with these polarization effects taken into account in a self-consistent way, the overall description of the discussed set of bands is not satisfactory.

In looking for an alternative physical scenario we have shown that another kind of crossing results from the signature-separation effect that shifts down the HF configurations with neutron-proton pairs present, with respect to those were such pairs are broken. Then the n-p paired configurations cross and interact, giving a correct qualitative reproduction of ${\cal J}^{(2)}$ in ⁶⁰Zn. This scenario has the advantage that the effect of interaction entirely disappears whenever an odd neutron or an odd proton blocks the n-p pairing interaction. Therefore, non-interacting configurations are obtained in odd neighbors of ⁶⁰Zn, yielding a perfect agreement with the data. This result was, however, obtained within a very simple two-band interaction and two-band mixing scheme, while the collective features of the T=0 n-p pairing were not studied. Whether or not such collective aspects of a simultaneous presence of the T=1 and T=0 pairing correlations are important will be the subject of future investigations.

This research was supported in part by the Polish Committee for Scientific Research (KBN) under Contract No. 5 P03B 014 21, by the French-Polish integrated actions program POLONIUM, and by the computational grants from the Regionales Hochschulrechenzentrum Kaiserslautern (RHRK) Germany and from the Interdisciplinary Centre for Mathematical and Computational Modeling (ICM) of the Warsaw University.