Charge radius of the short-lived ⁶⁸Ni and correlation with the dipole polarizability

We present the first laser spectroscopic measurement of the neutron-rich nucleus 68Ni at the N=40 subshell closure and extract its nuclear charge radius. Since this is the only short-lived isotope for which the dipole polarizability αD 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 48Ca. 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 68Ni