Microscopic analysis of prolate-oblate shape phase transition and shape coexistence in the Er-Pt region

The shape transition and possible occurrence of low-energy shape coexistence and rigid triaxial deformation are analyzed in the six even-even Er, Yb, Hf, W, Os, and Pt isotopic chains with the neutron number 102 <= N <= 124, using a five-dimensional collective Hamiltonian (5DCH) based on covariant density-functional theory. The potential-energy surfaces display a transition from prolate to oblate or triaxial, and then to near spherical shapes as the neutron number increases. The corresponding 5DCH model calculations reproduce the empirical isotopic trend of the characteristic collective observables and confirm the overall shape transition in this region. It is emphasized that a rapid shape transition between prolate and oblate shapes is predicted in Er and Yb isotopic chains while it becomes smooth for higher-Z isotopic chains and signature for rigid triaxial deformation is found in the transitional isotopes, e.g., W-194 and Os192-196 by analyzing the energy staggering and probability density distribution in the. bands. Finally, the calculated low-lying spectra for Er-184 and Yb-186 demonstrate a remarkable multishape coexistence of medium-deformed oblate, medium- and large-deformed prolate shapes in both nuclei.

Automated summary

The study uses a five-dimensional collective Hamiltonian to analyze the shape transition and possible low-energy shape coexistence in six even-even isotopic chains, showing a transition from prolate to oblate or triaxial shapes as neutron number increases. Model calculations reproduce empirical isotopic trends and reveal a rapid shape transition in certain isotopic chains, as well as signature for rigid triaxial deformation in transitional isotopes. The calculated low-lying spectra for specific nuclei demonstrate notable multishape coexistence.