Shape vibrations and quasiparticle excitations in the lowest 0+ excited state of the Erbium isotopes

TL;DR

This paper investigates the nature of the first excited 0+ states in Erbium isotopes, revealing a transition from shape fluctuation dominance in soft isotopes to quasiparticle dominance in well-deformed ones, using a generator coordinate method.

Contribution

It introduces a combined approach using shape fluctuations and quasiparticle states within the generator coordinate method to analyze 0+ states across Erbium isotopes.

Findings

First excited 0+ states are dominated by shape fluctuations in soft isotopes.

In well-deformed isotopes, two-quasiparticle states are more relevant.

A mixed degree of freedom is necessary for intermediate isotopes.

Abstract

The ground and first excited 0+ states of the {156-172}Er isotopes are analyzed in the framework of the generator coordinate method. The shape parameter beta is used to generate wave functions with different deformations which together with the two-quasiparticle states built on them provide a set of states. An angular momentum and particle number projection of the latter spawn the basis states of the generator coordinate method. With this ansatz and using the separable pairing plus quadrupole interaction we obtain a good agreement with the experimental spectra and E2 transition rates up to moderate spin values. The structure of the wave functions suggests that the first excited 0+ states in the soft Er isotopes are dominated by shape fluctuations, while in the well deformed Er isotopes the two-quasiparticle states are more relevant. In between both degrees of freedom are necessary .