Coupling of two-quasiparticle and collective excitations in Ge and Zn isotopes

Excitation energies and $B\left(E2\mathrm{}\right)\mathrm{}$ values of ${}_{}{}^{72}{}_{}{}^{}\mathrm{Ge}$, ${}_{}{}^{70}{}_{}{}^{}\mathrm{Zn}$, and ${}_{}{}^{74}{}_{}{}^{}\mathrm{Ge}$ are investigated by means of an extended generator coordinate method which allows in a microscopic way a simultaneous coupling of single particle and collective degrees of freedom. For the generating wave functions angular momentum and particle number projected Hartree-Fock-Bogoliubov solutions have been used. The low lying states of even parity and angular momentum are dominated by a coupling of shape vibrations and $K=0\mathrm{}$ two-quasiparticle excitations. In contrast to the yrast states especially the anomalously low lying first excited $0^{+}$ state in ${}_{}{}^{72}{}_{}{}^{}\mathrm{Ge}$ could only be explained by a strong coupling of both degrees of freedom. For ${}_{}{}^{72}{}_{}{}^{}\mathrm{Ge}$ and ${}_{}{}^{74}{}_{}{}^{}\mathrm{Ge}$, the most important contributions are due to the proton excitations, whereas in ${}_{}{}^{70}{}_{}{}^{}\mathrm{Zn}$, the neutron excitations play the dominant role.