Octupole correlations in superdeformed bands of $^{56}$Ni

The projected multi-dimensionally-constrained relativistic Hartree-Bogoliubov model was employed to calculate the potential energy surface of the high-spin states in $^{56}\text{Ni}$. It is pointed out for the first time that possible octupole deformations exist for the positive and negative parity superdeformed bands in $^{56}\text{Ni}$, with deformations $\beta_{30}\sim0.14$ and $\beta_{30}\sim0.24$, respectively, along with a large prolate deformation of $\beta_{20}\sim 0.42$. These octupole deformations are induced by the coupling between $2p_{3/2}$ and $1g_{9/2}$ orbits at the deformation $\beta_{20}\sim 0.4$. The calculated excitation energies of the two rotational bands are consistent with the observed superdeformed bands of $^{56}\text{Ni}$. In addition, two rotational bands are predicted, consisting of one superdeformed band with negative parity and one hyperdeformed bands with positive parity.