Deformation-driven intruder states in light island-of-inversion nuclei

Islands of inversion occur when the nuclear ground state is dominated by intruder configurations, specifically particle-hole excitations across shell gaps, rather than by the naive spherical shell-model expectation of filled shell configurations. Using the realistic and rigorous no-core shell model, we are able to confirm that deformation drives these intruder states in the light halo nuclides ¹¹Li and ²⁹F. In small model spaces, these deformed intruders lie high in energy with respect to spherical normal states; as the model space size increases, the intruders energetically approach, albeit slowly, the normal states. This provides further strong evidence of the connection between shape deformation/coexistence and islands of inversion, as well demonstrating as the computational challenges in rigorously modeling this phenomenon. Our results also suggest halo states can be strongly deformed and/or strongly mixed with normal spherical states.