Four-nucleon alpha-type correlations and proton-neutron pairing away of N=Z line

TL;DR

This paper investigates the competition between alpha-type quartets and proton-neutron pairing in nuclei away from the N=Z line, showing that alpha correlations are significant beyond self-conjugate nuclei.

Contribution

It introduces a ground state ansatz combining alpha-like quartets and excess pairs, accurately describing pairing energies in various nuclei.

Findings

Alpha-type correlations are important in nuclei away from N=Z.

The proposed ansatz yields accurate pairing energies.

Alpha-like quartets coexist with Cooper pairs in these nuclei.

Abstract

We study the competition between alpha-type and conventional pair condensation in the ground state of nuclei with neutrons and protons interacting via a charge-independent pairing interaction. The ground state is described by a product of two condensates, one of alpha-like quartets and the other one of pairs in excess relative to the isotope with N=Z. It is shown that this ansatz for the ground state gives very accurate pairing correlation energies for nuclei with the valence nucleons above the closed cores 16O, 40Ca and 100Sn. These results indicate that alpha-type correlations are important not only for the self-conjugate nuclei but also for nuclei away of N=Z line. In the latter case alpha-like quartets coexist with the collective Cooper pairs formed by the nucleons in excess.