Ground State Shape (Phase) Crossover in Er and Yb Isotopes

Ground-state shape (phase) crossover in Er and Yb isotopes is manifested in the axially deformed Nilsson mean-field plus extended pairing model. The energy ratio R_02⁺/21⁺, the odd-even mass differences and the information entropy are calculated under the present model, reproduce the shape (phase) crossover behaviors of these quantities in ^155-163Er and ^157-165Yb isotopes. From the analysis of these quantities as functions of the quadrupole deformation parameter and the overall pairing interaction strength, it is shown that the crossover is mainly driven by the competition between the pairing interaction and the quadrupole deformation, which thus provides the origin of the shape (phase) crossover in the present model.