Anomalous pairing vibration in neutron-rich Sn isotopes beyond the N=82 magic number

TL;DR

This paper investigates anomalous pairing vibrations in neutron-rich Sn isotopes beyond N=82, revealing enhanced pair transfer strengths and novel vibrational modes linked to weakly bound neutron orbits using microscopic models.

Contribution

It introduces a microscopic analysis of two-neutron transfer and identifies a new type of pair vibrational mode in neutron-rich Sn isotopes beyond N=82.

Findings

Enhanced pair transfer strength in isotopes with A ≥ 140.

Discovery of anomalous pair vibrational modes with extended transition densities.

Weakly bound neutron orbits are crucial for these phenomena.

Abstract

Two-neutron transfer associated with the pair correlation in superfluid neutron-rich nuclei is studied with focus on low-lying $0^+$ states in Sn isotopes beyond the N=82 magic number. We describe microscopically the two-neutron addition and removal transitions by means of the Skyrme-Hartree-Fock-Bogoliubov mean-field model and the continuum quasiparticle random phase approximation formulated in the coordinate space representation. It is found that the pair transfer strength for the transitions between the ground states becomes significantly large for the isotopes with $A \ge 140$, reflecting very small neutron separation energy and long tails of the weakly bound $3p$ orbits. In $^{132-140}$Sn, a peculiar feature of the pair transfer is seen in transitions to low-lying excited $0^+$ states. They can be regarded as a novel kind of pair vibrational mode which is characterized by an anomalously long tail of the transition density extending to far outside of the nuclear surface, and a large strength comparable to that of the ground-state transitions. The presence of the weakly bound neutron orbits plays a central role for these anomalous behaviors.