Generator coordinate method with proton–neutron pairing fluctuations and magnetic properties of N = Z odd–odd nuclei

Pairing correlations play an important role in a variety of nuclear phenomena. However, a quantitative understanding of proton–neutron (pn) pairing, especially isoscalar pn pairing (S = 1, T = 0) remains elusive. To clarify the property of pn pairing, we investigate the roles of pn pairing in the M1 transition of N = Z odd–odd nuclei. We develop a theoretical model based on the generator coordinate method (GCM) in which the isoscalar and isovector pn-pair amplitudes are used as the generator coordinates. Using the particle and the angular-momentum projections, the pn-pair GCM well reproduces the M1 transition of odd–odd nuclei for the exactly solvable SO(8) model. We apply the method to N = Z odd–odd nuclei and find that the experimental values of B(M1) are well reproduced. We also study the sensitivity of B(M1) to the strength of the isoscalar pairing interaction.