Ab Initio Study on the Halo Structure in ¹¹Be

We present an ab initio study on the one-neutron halo nucleus ¹¹Be using nuclear lattice effective field theory with high-fidelity chiral interactions at N3LO. By employing the wavefunction matching method to mitigate the sign problem and the pinhole algorithm to sample many-body correlations, we successfully reproduce the ground-state parity inversion and the extended matter radius characteristic of the halo structure. We analyze the intrinsic density distributions and geometric shapes of ¹¹Be in comparison with the core nucleus ¹⁰Be. Our results reveal a prominent two-cluster structure in both nuclei and the occupation of the (Formula presented.) molecular orbital by the valence neutron in ¹¹Be. It enhances the prolate deformation as well as the diffuse neutron tail, distinct from the (Formula presented.) -orbital occupation observed in the ¹⁰Be ground state.