Structure and reactions of the two-neutron halo nucleus ${}^{11}\text{Li}$

The two-neutron halo nucleus ${}^{11}\text{Li}$ represents one of the most striking manifestations of exotic nuclear structure far from stability. Its extremely low two-neutron separation energy, extended matter distribution, and Borromean three-body configuration (${n} + n + {}^{9}\text{Li}$) make it a benchmark system for studying weak binding, neutron correlations, and continuum effects. This review summarizes the experimental approaches that have elucidated the halo structure of ${}^{11}\text{Li}$, including interaction cross section measurements, elastic proton scattering, transfer reactions, momentum distribution analyses, Coulomb breakup. Particular emphasis is placed on the role of the unbound subsystem ${}^{10}\text{Li}$ in shaping the structure of ${}^{11}\text{Li}$ through its virtual $s$-states and low-lying resonances. The experimental findings are interpreted in the context of modern three-body theoretical models, highlighting the interplay between valence neutron correlations and nuclear dynamics at the edge of stability.