Ground state properties and possible octupole deformations of Sr, Zr, Mo, and Ru isotopic chains within the covariant energy density functional theory

Abstract

Reflection-asymmetric relativistic mean-field (RASRMF) theory is employed to systematically investigate the ground-state properties and the possible octupole deformations for the even-even Sr, Zr, Mo, and Ru isotopes with neutron number $N=30-60$. The calculated binding energies, quadrupole deformations, and charge radii agree with the experimental data as well as other theoretical calculations. Along all these chains, abrupt changes in the charge radius around $N=58$ occur due to significant variations in the ground state deformation. Notably, no octupole-deformed ground states are found in the potential energy surfaces of the Sr, Zr, Mo, and Ru isotopes with $N\approx 34$ and 56. The possible octupole-deformed nuclei are predicted in the light mass region with $N\approx Z\approx 40$, which agrees with the results from both relativistic Hartree-Bogoliubov (RHB) and nonrelativistic Hartree-Fock-Bogoliubov (HFB) calculations. The experimental fingerprints of octupole correlations around $N=40$ are convincing in the present calculations. In addition, we gain deeper insight into the octupole shape phase transition and shape coexistence within these isotopic chains.