A metallic p-wave magnet with commensurate spin helix

Antiferromagnetic states with a spin-split electronic structure give rise to spintronic, magnonic and electronic phenomena despite (near-)zero net magnetization^1-7. The simplest odd-parity spin splitting-p wave-was originally proposed to emerge from a collective instability in interacting electron systems^8-12. Recent theory has identified a distinct route to realize p-wave spin-split electronic bands without strong correlations^13,14, termed p-wave magnetism. Here we demonstrate an experimental realization of a metallic p-wave magnet. The odd-parity spin splitting of delocalized conduction electrons arises from their coupling to an antiferromagnetic texture of localized magnetic moments: a coplanar spin helix whose magnetic period is an even multiple of the chemical unit cell, as revealed by X-ray scattering experiments. This texture breaks space-inversion symmetry but approximately preserves time-reversal symmetry up to a half-unit-cell translation-thereby fulfilling the symmetry conditions for p-wave magnetism. Consistent with theoretical predictions, our p-wave magnet shows a characteristic anisotropy in the electronic conductivity^13-15. Relativistic spin-orbit coupling and a tiny spontaneous net magnetization further break time-reversal symmetry, resulting in a giant anomalous Hall effect (Hall conductivity >600 S cm^-1, Hall angle >3%), for an antiferromagnet. Our model calculations show that the spin-nodal planes found in the electronic structure of p-wave magnets are readily gapped by a small perturbation to induce the anomalous Hall effect. We establish metallic p-wave magnets as an ideal platform to explore the functionality of spin-split electronic states in magnets, superconductors, and in spintronic devices.