Enhancement of high-spin collectivity in N = Z nuclei by the isoscalar neutron–proton pairing

Pairing from different fermions, neutrons and protons, is unique in nuclear physics. The fingerprint for the isoscalar T=0T=0 neutron–proton (np) pairing has however remained a question. We study this exotic pairing mode in excited states of rotating N≈ZN≈Z nuclei by applying the state-of-the-art shell-model calculations for 88Ru and the neighboring 90,92Ru isotopes. We show that the T=0T=0 np pairing is responsible for the distinct rotational behavior between the N=ZN=Z and N>ZN>Z nuclei. Our calculation suggests a gradual crossover from states with mixed T=1T=1 and T=0T=0 pairing near the ground state to those dominated by the T=0T=0 np pairing at high spins. It is found that the T=0T=0 np pairing plays an important role in enhancing the high-spin collectivity, thereby reducing shape variations along the N=ZN=Z line.