Unveiling potential neutron halos in intermediate-mass nuclei: an \textit{ab initio} study

Halos epitomize the fascinating interplay between weak binding, shell evolution, and deformation effects, especially in nuclei near the drip line. In this Letter, we apply the state-of-the-art \textit{ab initio} valence-space in-medium similarity renormalization group approach to predict potential candidates for one- and two-neutron halo in the intermediate-mass region. Notably, we use spectroscopic factors (SF) and two-nucleon amplitudes (TNA) as criteria for suggesting one- and two-neutron halo candidates, respectively. This approach is not only theoretically sound but also amenable to experimental validation. Our research focuses on Mg, Al, Si, P, and S neutron-drip-line nuclei, offering systematic predictions of neutron halo candidates in terms of separation energies, SF (TNA), and average occupation. The calculation suggests the ground states of $^{40,42,44,46}$Al, $^{41,43,45,47}$Si, $^{46,48}$P, and $^{47,49}$S are promising candidates for one-neutron halos, while $^{40,42,44,46}$Mg, $^{45,47}$Al, $^{46,48}$Si, $^{49}$P, and $^{50}$S may harbor two-neutron halos. In addition, the relative mean-square neutron radius between halo nuclei and \textit{inner core} is calculated for suggested potential neutron halos. Finally, the relations of halo formations and shell evolution are discussed.