Shell-model-like approach based on cranking covariant density functional theory: bandcrossing and shape evolution in $^{60}$Fe

TL;DR

This paper develops a covariant density functional theory-based shell-model-like approach to study rotational structures, bandcrossings, and shape evolution in neutron-rich $^{60}$Fe, accurately reproducing experimental spectra without ad hoc parameters.

Contribution

It introduces a self-consistent, parameter-free method combining covariant density functional theory with shell-model concepts to analyze rotational bands and shape changes in $^{60}$Fe.

Findings

Reproduces experimental rotational spectra and band structures of $^{60}$Fe.

Identifies bandcrossing mechanisms involving neutron orbital changes.

Shows deformation parameters vary with rotational frequency and differ among bands.

Abstract

The shell-model-like approach is implemented to treat the cranking many-body Hamiltonian based on the covariant density functional theory including pairing correlations with exact particle number conservation. The self-consistency is achieved by iterating the single-particle occupation probabilities back to the densities and currents. As an example, the rotational structures observed in the neutron-rich nucleus $^{60}$Fe are investigated and analyzed. Without introducing any \emph{ad hoc} parameters, the bandheads, the rotational spectra, and the relations between the angular momentum and rotational frequency for the positive parity band A, and negative parity bands B and C are well reproduced. The essential role of the pairing correlations is revealed. It is found that for band A, the bandcrossing is due to the change of the last two occupied neutrons from the $1f_{5/2}$ signature partners to the $1g_{9/2}$ signature partners. For the two negative parity signature partner bands B and C, the bandcrossings are due to the pseudo-crossing between the $1f_{7/2,~5/2}$ and the $1f_{5/2,~1/2}$ orbitals. Generally speaking, the deformation parameters $\beta$ for bands A, B, and C decrease with rotational frequency. For band A, the deformation jumps from $\beta\sim0.19$ to $\beta\sim0.29$ around the bandcrossing. In comparison with its signature partner band C, band B exhibits appreciable triaxial deformation.