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

Experimentally observed superdeformed(SD) rotational bands in ~(36)Ar and ~(40)Ar 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 ω =1.5 Me V in ~(36)Ar is attributed to the sharp rise of the simultaneous alignments of the neutron and proton 1 d_(5/2)[202]5/2 pairs and 1 f_(7/2)[321]3/2 pairs, which is a consequence of the band crossing between the 1 d_(5/2)[202]5/2 and 1 f_(7/2)[321]3/2 configuration states. The gentle upbending at low frequency of the SD band in ~(40)Ar is mainly affected by the alignments of the neutron 1 f_(7/2)[321]3/2 pairs and proton 1 d_(5/2)[202]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.