Mixing of quasiparticle excitations and γ vibrations in transitional nuclei

Evidence of strong coupling of quasiparticle excitations with γ vibration is shown to occur in transitional nuclei. High-spin band structures in 166,168,170,172Er are studied by employing the recently developed multiquasiparticle triaxial projected shell model approach. It is demonstrated that a low-lying $K=3$ band observed in these nuclei, the nature of which has remained unresolved, originates from the angular-momentum projection of triaxially deformed two-quasiparticle (qp) configurations. Furthermore, it is predicted that the structure of this band depends critically on the shell filling: in ¹⁶⁶Er the lowest $K=3$ 2-qp band is formed from proton configuration, in ¹⁶⁸Er the $K=3$ neutron and proton 2-qp bands are almost degenerate, and for ¹⁷⁰Er and ¹⁷²Er the neutron $K=3$ 2-qp band becomes favored and can cross the γ-vibrational band at high rotational frequencies. We consider that these are a few examples in even-even nuclei, where the three basic modes of rotational, vibrational, and quasiparticle excitations coexist close to the yrast line.