Microscopic restoration of proton-neutron mixed symmetry in weakly collective nuclei

Starting from the microscopic low-momentum nucleon-nucleon interaction V-lowk, we present a systematic shell-model study of magnetic moments and magnetic dipole transition strengths of the basic low-energy one-quadrupole phonon excitations in nearly spherical nuclei. Studying in particular the even-even N=52 isotones from Zr-92 to Cd-100, we find the predicted evolution of the predominantly proton-neutron nonsymmetric state reveals a restoration of collective proton-neutron mixed-symmetry structure near midshell. This provides a quantitative explanation for the existence of pronounced collective mixed-symmetry structures in weakly collective nuclei.