Exploring nuclear multiple chirality in the $A\approx 60$ mass region within covariant density functional theory

The nuclear multiple chirality in $A\approx 60$ mass region is explored by the adiabatic and configuration-fixed constrained covariant density functional theory for cobalt isotopes. The potential-energy curves and triaxiality parameters $\gamma$ as functions of the deformation parameter $\beta$ in ${}^{54,56,57,58,59,60}\mathrm{Co}$ are obtained. It is found that there are high-$j$ particle(s) and hole(s) configurations with prominent triaxially deformed shapes in these isotopes. This points towards that the existence of chirality or multiple chirality in $A\approx 60$ mass region are highly anticipated.

Figure 1

Single-proton (left column) and single-neutron (right column) Routhians near the Fermi surface in ${}^{54–60}\mathrm{Co}$ for the ground state.

Figure 2

The potential-energy curves in adiabatic (open circles) and configuration-fixed (solid lines) constrained triaxial CDFT calculation with PC-PK1 for ${}^{54–60}\mathrm{Co}$. The local minima in the energy surfaces for fixed configuration are represented as stars and labeled, respectively, as A, B, C, and D.

Figure 3

The calculated energy spectra by particle rotor model in comparison with the experimental data in Ref. [65]. More details can be seen in the text.

Figure 4

The triaxiality parameter $\gamma$ (in degrees) as a function of the deformation parameter $\beta$ in adiabatic (open circles) and configuration-fixed (solid lines) constrained triaxial CDFT calculations based on the PC-PK1 interaction for ${}^{54–60}\mathrm{Co}$. The local minima in the energy curves for fixed configurations are indicated by stars and labeled as A, B, C, and D in accordance with the increasing of energy, respectively. The shaded area represents the triaxiality parameter $\gamma$ favorable for nuclear chirality.

Figure 5

The ratio $Z/N$ of proton number and neutron number of Co isotopes are compared with those of reported chiral nuclei and $\mathrm{M}\chi \mathrm{D}$ nuclei in the $A\approx 80,100,130$, and 190 mass regions. The data are from Ref. [10] and references therein.