Nuclear superdeformation is a unique testing ground for the shell structure at extreme deformation. In the light mass region, superdeformed (SD) states were investigated along the N=Z line and a new ‘island’ of SD nuclei was found around A～40 nuclei (i.e., 36Ar[1], 40Ca[2], and 44Ti[3]). Presences of these SD bands indicate the SD shell gaps at N=Z=18, 20, and 22. To clarify the SD shell structures in neutron-rich side, high-spin states in 40Ar were investigated[4], where SD bands associated with asymmetric combination of SD magic numbers, Z=18 and N=22 are expected. High-spin states of other nuclei in A=30～40 region were also studied, including 42Ca associated with the Z=20 and N=22 SD magic numbers and 35S, 36Cl. In the talk, recent experimental results of the SD band in 40Ar and high-spin level structures in A=30～40 will be presented. In order to extend these studies to neutron-rich side, future high-spin studies using energy-degraded RI beams will be also discussed.
[1] C.E. Svensson et al., Phys. Rev. Lett. 85, 2693 (2000).
[2] E. Ideguchi et al., Phys. Rev. Lett. 87, 222501 (2001).
[3] C.D. O'Leary et al., Phys. Rev. C 61, 064314 (2000).
[4] E. Ideguchi et al., Phys. Lett. B 686, 18 (2010).