While the phenomenon of one- and two-neutron ground-state halo nuclei is well established, the effects of weak binding on the low-lying excitation spectrum remain largely unexplored. To address this interesting question, we have studied the coupling of weakly bound (halo) valence neutrons to a deformed core using a Weak-Coupling phenomenological approach and the ParticleRotor model. “Universal” indicators that relate the 2n separation energy to the volume overlap between the core and halo can be used to characterize and identify possible halo nuclei. Our results are contrasted to the known properties of 38,40Mg, to assess the impact of weak binding on the low-lying excitation spectrum, one-proton removal reaction cross-sections and transition probabilities. Despite its simplicity, the phenomenological model appears to capture the main physical ingredients and provides a framework that allows us to examine possible coupling schemes involving a core and a 2n halo. Other approaches to the structure of 40Mg exist that differ in the nature of the second experimental γ transition. Further experimental and theoretical works will be required to elucidate their intriguing structure, which we trust will be motivated by this work.
