By Yue Shi, J.C. Pei and F.R. Xu at School of Physics, Peking University,

J. Dobaczewski at University of Warsaw, Poland,

S. Frauendorf at University of Notre Dame, USA,

W. Nazarewicz and N. Nikolov at University of Tennessee, USA

Stimulated by recent experimental discoveries, triaxial strongly deformed (TSD) states in Er-158 at ultrahigh spins have been studied by means of the Skyrme-Hartree-Fock model and the tilted-axis-cranking method. Restricting the rotational axis to one of the principal axes—as done in previous cranking calculations—two well-defined TSD minima in the total Routhian surface are found for a given configuration: one with positive and another with negative triaxial deformation gamma. By allowing the rotational axis to change direction, the higher-energy minimum is shown to be a saddle point. This resolves the long-standing question of the physical interpretation of the two triaxial minima at a very similar quadrupole shape obtained in the principal-axis-cranking approach. Several TSD configurations have been predicted, including a highly deformed band, which is a candidate for the structure observed in experiment. This work has been published recently in Physical Review Letters 108, 092501 (2012).

This work has been supported by the Natural Science Foundation of China, U.S. Department of Energy, Academy of Finland and University of Jyväskylä.