Pairing correlations in high-spin isomers

High-spin isomers with J(pi)=49/2(+) and 27(+) have been systematically observed in a number of N=83 isotones with 60 <= Z <= 67 at excitation energies similar to 9 MeV. Based on experimental excitation energies, an odd-even binding energy staggering has been extracted for the first time for these multi-quasiparticle states. Surprisingly, the magnitude of the odd-even effect in high-spin isomers turned out to be very close to that in ground states, thus challenging conventional wisdom that pairing correlations are reduced in highly excited states. Theoretical analysis based on mean-field theory explains the observed proton number dependence of the odd-even effect as a manifestation of strong pairing correlations in the highly excited states. Mean-field effects and the proton-neutron residual interaction on the odd-even staggering are also examined.