Frustrated spin-1/2 chains in a correlated metal

Electronic correlations lead to heavy quasiparticles in three-dimensional (3D) metals, and their collapse can destabilize magnetic moments. It is an open question whether there is an analogous instability in one-dimensional (1D) systems, unanswered due to the lack of metallic spin chain materials. We report neutron scattering measurements and density matrix renormalization group calculations establishing spinons in the correlated metal Ti₄MnBi₂, confirming that its magnetism is 1D. Ti₄MnBi₂ is inherently frustrated, forming near a quantum critical point that separates different phases at temperature T = 0. One-dimensional magnetism dominates at the lowest T, and is barely affected by weak interchain coupling. Ti₄MnBi₂ is a previously unrecognized metallic spin chain in which 3D conduction electrons become strongly correlated due to their coupling to 1D magnetic moments.