Multiphonon γ -vibrational bands and the triaxial projected shell model

We present a fully quantum-mechanical, microscopic, unified treatment of ground-state band and multiphonon γ-vibrational bands using shell model diagonalization with the triaxial projected shell model. The results, which agree very well with data on the g- and γ-band spectra in ^156-170Er, as well as with recently measured 4⁺ two-phonon γ-bandhead energies in ¹⁶⁶Er and ¹⁶⁸Er, are discussed in terms of the K mixing. Multiphonon γ-excitation energies are predicted.