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 σ molecular orbital by the valence neutron in 11Be. It enhances the prolate deformation as well as the diffuse neutron tail, distinct from the π-orbital occupation observed in the 10Be ground state.