Recent experimental studies on proton-rich nuclei in the $sd$ shell have revealed intriguing near-threshold phenomena, including exotic structures associated with mirror symmetry breaking. In particular, a halolike structure has been suggested for the $1^{+}$ state of ${}^{22}\mathrm{Al}$ based on the large isospin asymmetry observed in the ${}^{22}\mathrm{Si}/{}^{22}\mathrm{O}$ mirror Gamow-Teller transitions. Recent mass measurements further indicate that the ground state of ${}^{22}\mathrm{Al}$ is weakly bound, with a single-proton separation energy of about 100 keV. To investigate how the continuum affects the structure and decay properties of this proton-dripline nucleus, we employ the state-of-the-art Gamow shell model. This approach utilizes valence-space effective interactions and operators derived from chiral forces. Our calculations identify the ground state of ${}^{22}\mathrm{Al}$ as a $4^{+}$ state, with a $3^{+}$ state as the first excitation. Despite their diffuse nature under weak binding, the Thomas-Ehrman shift for these states is found to be negligible due to their small $s$-wave components. In contrast, the excited $1_1^{+}$ state possesses a significantly larger $s$-wave component, resulting in a more pronounced halolike structure.

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• Effective field theory
• Electromagnetic transitions
• Nuclear structure & decays
• 20 ≤ A ≤ 38
• Shell model