Low-frequency $K^{\pi}=0^{+}$ modes in deformed neutron-rich nuclei: Pairing- and $\beta$-vibrational modes of neutron

TL;DR

This paper investigates low-frequency $K^{}^{+}$ modes in deformed neutron-rich nuclei using quasiparticle-random-phase approximation, revealing strongly collective modes enhanced by neutron wave function extension and pairing fluctuations.

Contribution

It introduces a detailed analysis of $K^{}^{+}$ modes in neutron-rich nuclei, highlighting the role of neutron wave functions and pairing fluctuations in mode collectivity.

Findings

Strongly collective $K^{}^{+}$ modes found in Mg, Cr, and Fe isotopes.

Neutron wave function extension enhances transition strengths.

Pairing field fluctuations induce coherence among two-quasiparticle excitations.

Abstract

Low-frequency $K^{\pi}=0^{+}$ states in deformed neutron-rich nuclei are investigated by means of the quasiparticle-random-phase approximation based on the Hartree-Fock-Bogoliubov formalism in the coordinate space. We have obtained the very strongly collective $K^{\pi}=0^{+}$ modes not only in neutron-rich Mg isotope but also in Cr and Fe isotopes in N=40 region, where the onset of nuclear deformation has been discussed. It is found that the spatially extended structure of neutron quasiparticle wave functions around the Fermi level brings about a striking enhancement of the transition strengths. It is also found that the fluctuation of the pairing field plays an important role in generating coherence among two-quasiparticle excitations of neutron.