Evidence for the microscopic formation of mixed-symmetry states from magnetic moment measurements

Abstract

Using the transient field technique, the magnetic moments of the second excited ${2}^{+}$ states in $^{92,94}\mathrm{Zr}$ have been measured for the first time. The large positive $g$ factors, $g({2}_{2}^{+};{}^{92}\mathrm{Zr})=+0.76(50)$ and $g({2}_{2}^{+};{}^{94}\mathrm{Zr})=+0.88(27)$, which are in contrast to the known negative $g$ factors of the ${2}_{1}^{+}$ states, are found to be a consequence of weak proton-neutron coupling combined with the $Z=40$ subshell closure. From their large $M1$ transition strengths to the ${2}_{1}^{+}$ states, in earlier works an assignment to the ${2}_{2}^{+}$ states as proton-neutron symmetric and mixed-symmetry states has been made, which are now found to be polarized in their proton-neutron content. This fact allows to identify the underlying microscopic main configurations in the wave functions, which form the building blocks of symmetric and mixed-symmetry states in this region as valence nucleons are added and shell structure changes.