Charge radius of the short-lived ${}^{68}$Ni and correlation with the dipole polarizability

Abstract

We present the first laser spectroscopic measurement of the neutron-rich nucleus ${}^{68}$Ni at the \mbox{$N=40$} subshell closure and extract its nuclear charge radius. Since this is the only short-lived isotope for which the dipole polarizability ${\alpha }_{\mathrm{D}}$ has been measured, the combination of these observables provides a benchmark for nuclear structure theory. We compare them to novel coupled-cluster calculations based on different chiral two- and three-nucleon interactions, for which a strong correlation between the charge radius and dipole polarizability is observed, similar to the stable nucleus ${}^{48}$Ca. Three-particle--three-hole correlations in coupled-cluster theory substantially improve the description of the experimental data, which allows to constrain the neutron radius and neutron skin of ${}^{68}$Ni.

6 pages, 3 figures