Pairing and rotation in 74Rb

Recently, the experimental identification of T = 0 and T = 1 bands was reported in the N = Z = 37 nucleus 74Rb. The ground-state rotational band was interpreted as being formed from the T = 1 isobaric analogue states of 74Kr. But at higher excitation energy a T = 0 rotational band becomes energetically favoured over the T = 1 ground-state band. It is also well known that the structure of the odd-odd and even-even N ≅ Z nuclei in the A = 70 region is dominated by shape coexistence phenomena. In order to get a realistic description of the structure of 74Rb we used the 'complex' version of the EXCITED VAMPIR model employing chains of variational calculations based on symmetry-projected essentially 'complex' Hartree-Fock-Bogoliubov vacua including neutron-proton pairing in both T = 0 and T = 1 channels and unnatural-parity correlations. In order to have a more direct access to the competition between like-nucleon isovector pairing on one hand, and the isovector and isoscalar neutron-proton pairing on the other hand, we investigated particular parts of the two-body densities which are expected to reflect these aspects, as well as the effects of changes in the two-body interaction on the resulting many-body wave functions. The calculations suggest that while the yrast states up to spin 12+ are based mainly on prolate deformed configurations, the corresponding first excited states are based on oblate deformed ones. For higher spins the oblate minimum is going higher in energy. The oblate configuration represents about 30% for the ground state, is decreasing to 20% for spin 2+ and, essentially, is disappearing at spin 8+. The structure of the ground-band states is dominated by the isovector Jπ = 0+ neutron-proton pairing correlations at low spins and by the aligned pairs at intermediate spins. The pair structure of the wave functions indicates a strong dependence on the deformation. With increasing spin a clear correlation between the reduction of the amount of isovector neutron-proton Jπ = 0+ pairs and the rising of the number of the aligned isovector Jπ = 8+ and isoscalar Jπ 9+ pairs is revealed by the structure of the yrast even spin states. (authors)