Microscopic analysis of shape transition in neutron-deficient Yb isotopes

Abstract

The development of nuclear collectivity in even-even $^{152\text{--}170}\mathrm{Yb}$ is studied with three types of mean-field calculations: the nonrelativistic Hartree-Fock plus BCS calculation using the Skyrme SLy4 force plus a density-dependent $\ensuremath{\delta}$ pairing force and the relativistic mean-field calculation using a point-coupling energy functional supplemented with either a density-independent $\ensuremath{\delta}$ pairing force or a separable pairing force. The low-lying states are obtained by solving a five-dimensional collective Hamiltonian with parameters determined from the three mean-field solutions. The energy surfaces, excitation energies, electric multiple transition strengths, and differential isotope shifts are presented in comparison with available data. Our results show that different treatments of pairing correlations have a significant influence on the speed of developing collectivity as the increase of neutron number. All the calculations demonstrate the important role of dynamic shape-mixing effects in resolving the puzzle in the dramatic increase of charge radius from $^{152}\mathrm{Yb}$ to $^{154}\mathrm{Yb}$ and the role of triaxiality in $^{160,162,164}\mathrm{Yb}$.