Ultrahigh Spin Structures in ^157,158,159Er

Rotational structures at ultrahigh spin in ^157,158,159Er have been investigated with the configuration-dependent cranked Nilsson--Strutinsky approach. Configurations of observed bands are assigned and the corresponding deformations are given theoretically. The calculations suggest that one of ultrahigh spin bands in ¹⁵⁸Er is triaxial highly deformed and the other is normal-deformed, while both ultrahigh spin bands in ¹⁵⁷Er are suggested to be triaxial highly deformed. The possible ultrahigh spin bands in ¹⁵⁹Er are predicted to be triaxial highly deformed and have shape coexistence in the same configuration. The configurations with two neutron holes in the N_osc=4 orbitals and two neutron holes in the h_11/2 orbitals in ¹⁵⁹Er are favoured for ultrahigh spin states but unfavoured for band termination, which is similar to ultrahigh spin bands in ^157,158Er.