Understanding Xe isotopes near $A=130$ through the prolate-oblate shape phase transition

Abstract

A simple algebraic scheme incorporating the prolate-oblate shape phase transition (SPT) is proposed within the framework of the interacting boson model to describe the quadrupole deformation features of Xe isotopes near $A=130$. The analysis demonstrates that novel $\gamma$-soft modes, characterized by the unusual quadrupole moments $Q(2_1^+)<0$ and $0<Q(2_2^+)\ll |Q(2_1^+)|$, can emerge near the critical point of this SPT. This finding is further applied to interpret the properties of low-lying states in the relevant Xe nuclei, particularly the experimentally observed nearly vanishing spectroscopic quadrupole moment $Q(2_2^+)$, thereby offering new insights into the structure of a $\gamma$-soft deformed nucleus.