Interacting-boson-fermion-approximation description of negative-parity states in even-odd Yb isotopes

The negative-parity energy levels of the even-odd Yb isotopes, ${}_{}{}^{163}{}_{}{}^{}\mathrm{Yb}$, ${}_{}{}^{165}{}_{}{}^{}\mathrm{Yb}$, ${}_{}{}^{169}{}_{}{}^{}\mathrm{Yb}$, ${}_{}{}^{171}{}_{}{}^{}\mathrm{Yb}$, and ${}_{}{}^{173}{}_{}{}^{}\mathrm{Yb}$, are studied systematically within the framework of the extended interacting-boson-fermion-approximation (IBFA) model in which one odd fermion is couplied with a boson core. The boson core is described with the IBA model but allowing one boson to break into a quasifermion pair. The odd fermion is assumed to be in one of the ${\mathit{f}}_{7/2}$ and ${\mathit{p}}_{3/2}$ single-particle orbitals while the fermion pair is allowed to occupy the single-particle orbit ${\mathit{i}}_{13/2}$. It was found that the negative-parity energy levels of these even-odd Yb isotopes and the values of transition quadrupole moments for the ground-state rotational band of ${}_{}{}^{173}{}_{}{}^{}\mathrm{Yb}$ can be reproduced in fairly good agreement with the observed data.