Enhanced collectivity in neutron-deficient Sn isotopes in energy functional based collective Hamiltonian

TL;DR

This study uses a collective Hamiltonian based on relativistic mean-field calculations to successfully reproduce and explain the enhanced collectivity and E2 transition strengths in neutron-deficient Sn isotopes, highlighting the role of neutron level degeneracy and pairing.

Contribution

It introduces a novel approach combining a five-dimensional collective Hamiltonian with relativistic mean-field parameters to explain enhanced collectivity in Sn isotopes.

Findings

Reproduces excitation energies and B(E2) values accurately.

Identifies neutron level degeneracy as a key factor.

Shows increased shape fluctuations lead to enhanced collectivity.

Abstract

The low-lying collective states in Sn isotopes are studied by a five-dimensional collective Hamiltonian with parameters determined from the triaxial relativistic mean-field calculations using the PC-PK1 energy density functional. The systematics for both the excitation energies of $2^+_1$ states and $B(E2;0^+_1\to 2^+_1)$ values are reproduced rather well, in particular, the enhanced E2 transitions in the neutron-deficient Sn isotopes with N<66. We show that the gradual degeneracy of neutron levels 1g7/2 and 2d5/2 around the Fermi surface leads to the increase of level density and consequently the enhanced paring correlations from N=66 to 58. It provokes a large quadrupole shape fluctuation around the spherical shape, and leads to an enhanced collectivity in the isotopes around N=58.