Spherical-deformed shape coexistence for thepfshell 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 ${}^{54}\mathrm{Fe}.$ 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 ${}^{54}\mathrm{Fe},$ which is related to the deformed band of doubly magic ${}^{56}\mathrm{Ni}.$ 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.