  Evidence of strong coupling of quasiparticle excitations with gamma-vibration
is shown to occur in transitional nuclei. High-spin band structures in
[166,168,170,172]Er are studied by employing the recently developed
multi-quasiparticle 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. Further, it is
predicted that the structure of this band depends critically on the shell
filling: in [166]Er the lowest K=3 2-qp band is formed from proton
configuration, in [168]Er the K=3 neutron and proton 2-qp bands are almost
degenerate, and for [170]Er and [172]Er the neutron K=3 2-qp band becomes
favored and can cross the gamma-vibrational band at high rotational
frequencies. We consider that these are few examples in even-even nuclei, where
the three basic modes of rotational, vibrational, and quasi-particle
excitations co-exist close to the yrast line.
