Triaxiality in the Low-Lying Quadrupole Bands of Even–Even Yb Isotopes

Following a series of successful applications to the neighboring isotopic chains of the rare-earth region, a mean-field-derived IBM-1 Hamiltonian with an intrinsic triaxial deformation derived from fermionic proxy-SU(3) irreducible representations (irreps) is employed for the study of energies and B(E2) transition strengths in the low-lying quadrupole bands of the even–even 162–182Yb. Proxy-SU(3) next-highest-weight irreps are incorporated in the calculations for the first time, leading to a significantly improved agreement with experimental data, where available, compared to axially symmetric calculations, as well as to triaxial calculations considering only highest-weight irreps.