Backbendings of superdeformed bands in ~(36,40)Ar

Experimentally observed superdeformed (SD) rotational bands in ³⁶Ar and ⁴⁰Ar are studied by the cranked shell model (CSM) with the pairing correlations treated by a particle-number-conserving (PNC) method. This is the first time that PNC-CSM calculations have been performed on the light nuclear mass region around A=40. The experimental kinematic moments of inertia J⁽¹⁾ versus rotational frequency are reproduced well. The backbending of the SD band at frequency around hω=1.5 MeV in ³⁶Ar is attributed to the sharp rise of the simultaneous alignments of the neutron and proton 1d_5/2202]5/2 pairs and 1f_7/2321]3/2 pairs, which is a consequence of the band crossing between the 1d_5/2202]5/2 and 1f_7/2321]3/2 configuration states. The gentle upbending at low frequency of the SD band in ⁴⁰Ar is mainly affected by the alignments of the neutron 1f_7/2321]3/2 pairs and proton 1d_5/2202]5/2 pairs. The PNC-CSM calculations show that besides the diagonal parts, the off-diagonal parts of the alignments play an important role in the rotational behavior of the SD bands.