Di-neutron correlation in soft octupole excitations of neutron-rich Ni isotopes beyond N=50

TL;DR

This paper studies low-lying octupole excitations in neutron-rich Ni isotopes beyond N=50, revealing a neutron mode influenced by di-neutron correlations due to weak neutron binding.

Contribution

It introduces a detailed analysis of di-neutron correlations in soft octupole excitations using Skyrme-Hartree-Fock-Bogoliubov and continuum QRPA methods.

Findings

Neutron mode appears above neutron separation energy.

Strong influence of di-neutron correlation on excitations.

Weak neutron binding enhances di-neutron effects.

Abstract

We investigate low-lying octupole response of neutron-rich Ni isotopes beyond the N=50 shell closure using the Skyrme-Hartree-Fock-Bogoliubov mean-fields and the continuum quasi-particle random phase approximation. Performing detailed numerical analyses employing the Skyrme parameter set SLy4 and a density-dependent delta interaction of the mixed type, we show that a neutron mode emerges above the neutron separation energy as a consequence of the weak binding of neutrons and it exhibits strong influences of the di-neutron correlation.