Thermal properties of N=40 isotones

Using the shell-model Monte Carlo method, we study the thermal properties of four N=40 medium-mass nuclei: 68Ni, a substantially spherical and weakly paired nucleus; 70Zn, a superfluid spherical nucleus; 72Ge, a superfluid deformed nucleus which exhibits shape-coexistence; and the well-deformed, weakly-paired nucleus 80Zr. We investigate the competition between shape deformations and pairing correlations as a function of temperature. We find that shape and pairing changes contribute to the specific heat of the nucleus in a different way. While the superfluid-to-normal transition manifests itself as a pronounced peak in the specific heat around T=0.6-0.7MeV, the deformed-to-spherical transition is more gradual.