Collective modes of excitation in $^{64}Cu$.

Medium- and high-spin level sequences in $^{64}Cu$ were investigated using the complex $^{26}Mg(^{48}Ca$, $\alpha p5n\gamma)$ multinucleon transfer reaction. The experiment was performed with ATLAS accelerator facility at the Argonne National Laboratory using the Gammasphere array and the fragment mass analyzer (FMA). Two high-spin, quasirotational bands consisting of $stretched-E2$ transitions were observed in coincidence with the known low-spin structure for the first time. These bands share remarkable similarities with highly deformed and/or superdeformed bands observed in the $A\approx$ 60--70 mass region. In addition, a regular dipole sequence with weak $E2$ crossover transitions was observed as well. A general discussion of the observed structures, complemented by theoretical calculations within the framework of the adiabatic and configuration-fixed constrained covariant density functional theory and the quantum particle-rotor model are presented in the context of shell-structure evolution and the collectivity in the mass region.