Speaker
Description
We study even-even superheavy nuclei $(104 \leq Z \leq 126,\, N \leq 258)$ using a five-dimensional collective Hamiltonian based on triaxial relativistic Hartree-Bogoliubov calculations with the PC-PK1 functional, explicitly incorporating quantum shape fluctuations (QSFs) beyond the mean-field. The model accurately reproduces binding, separation, and $\alpha$-decay energies. A shape evolution from prolate deformation $(N \approx 150, 210)$ to $\gamma$-soft configurations $(N \approx 176, 246)$ and finally to spherical shapes $(N \approx 184, 258)$ is revealed. Remarkably, many transitional nuclei lack bound $0^+$ states because shallow fission saddles and QSF-induced zero-point vibrations prevent their stabilization. QSFs also smooth shell gaps, shifting the effective neutron closures from $N=184$ and 258 to $N=182$ and 256. Our results highlight the decisive role of QSFs in the stability of superheavy nuclei.