Quadrupole collectivity and shell closure in neutron-rich nuclei near N=126

We present a comprehensive study on the low-lying states of neutron-rich Er, Yb, Hf, and W isotopes across the N = 126 shell with a multireference covariant density functional theory. Beyond-mean-field effects from shape mixing and symmetry restoration on the observables that are relevant for understanding quadrupole collectivity and underlying shell structure are investigated. The general features of low-lying states in closed-shell nuclei are retained in these four isotopes around N = 126, even though the shell gap is overall quenched by about 30% with the beyond-mean-field effects. These effects are consistent with the previous generator-coordinate calculations based on Gogny forces, but much smaller than that predicted by the collective Hamiltonian calculation. It implies that the beyond-mean-field effects on the r-process abundances before the third peak at A approximate to 195 might be more moderate than that reported by Arcones and Bertsch [Phys. Rev. Lett. 108, 151101 (2012)].