Spherical-deformed shape coexistence for the pf shell in the nuclear shell model

A spherical-deformed shape coexistence for semimagic pf-shell nuclei is investigated. Deformed states can arise by breaking the f_7/2 submagic shell, and coexist with spherical yrast states for ⁵⁴Fe. These states are shown to be primarily two-particle two-hole excitations on top of the respective correlated ground states. In addition to these modes, a four-particle–four-hole excitation can be found for ⁵⁴Fe, which is related to the deformed band of doubly magic ⁵⁶Ni. To investigate this shape coexistence, we use the conventional shell-model diagonalization, constrained Hartree-Fock, generator coordinate, variation-after-projection, and Monte Carlo shell-model methods.