Triaxial projected shell model study of γ-vibrational bands in even-even Er isotopes

We expand the triaxial projected shell model basis to include triaxially deformed multi-quasiparticle states. This allows us to study the yrast and γ-vibrational bands up to high spins for both γ-soft and well-deformed nuclei. As a first application, a systematic study of the high-spin states in Er isotopes is performed. The calculated yrast and γ bands are compared with the known experimental data, and it is shown that the agreement between theory and experiment is quite satisfactory. The calculation leads to predictions for bands based on one- and two-γ phonons where current data are still sparse. It is observed that γ bands for neutron-deficient isotopes of ¹⁵⁶Er and ¹⁵⁸Er are close to the yrast band, and further these bands are predicted to be nearly degenerate for high-spin states.