Deformability of neutron-deficient Sn nuclei studied with semi-realistic interaction

Although Sn nuclei have long been considered typical spherical nuclei, the $E2$ transitions in neutron-deficient Sn nuclei have posed a puzzle. We argue that their deformability may resolve this issue, based on self-consistent calculations with a semi-realistic interaction. The significant role of the pseudo-spin symmetry, which is attributed to the effects of the tensor force, is also discussed.