  The low-spin structure of the semimagic 64Ni nucleus has been considerably
expanded: combining four experiments, several 0+ and 2+ excited states were
identified below 4.5 MeV, and their properties established. The Monte Carlo
shell model accounts for the results and unveils an unexpectedly complex
landscape of coexisting shapes: a prolate 0+ excitation is located at a
surprisingly high energy (3463 keV), with a collective 2+ state 286 keV above
it, the first such observation in Ni isotopes. The evolution in excitation
energy of the prolate minimum across the neutron N = 40 subshell gap highlights
the impact of the monopole interaction and its variation in strength with N.
