Metallic $p$-wave magnet with commensurate spin helix

TL;DR

This paper reports the experimental realization of a metallic $p$-wave magnet where conduction electrons exhibit odd-parity spin splitting due to coupling with a specific antiferromagnetic spin helix, leading to unique electronic and Hall effects.

Contribution

It demonstrates a new type of $p$-wave magnetism in a metallic system driven by antiferromagnetic texture, confirming theoretical predictions with experimental evidence.

Findings

Observation of odd-parity spin splitting in conduction electrons

Anisotropic electronic conductivity consistent with $p$-wave magnetism

Giant anomalous Hall effect induced by spin-orbit coupling and broken $T$ symmetry

Abstract

Antiferromagnetic states with spin-split electronic structure give rise to novel spintronic, magnonic, and electronic phenomena despite (near-) zero net magnetization. The simplest odd-parity spin splitting - $p$-wave - was originally proposed to emerge from a collective instability in interacting electron systems. Recent theory identifies a distinct route to realise $p$-wave spin-split electronic bands without strong correlations, termed $p$-wave magnetism. Here we demonstrate an experimental realisation of a metallic $p$-wave magnet. The odd-parity spin splitting of delocalised conduction electrons arises from their coupling to an antiferromagnetic texture of localised 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 preserves time-reversal ($T$) 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 exhibits a characteristic anisotropy in the electronic conductivity. Relativistic spin-orbit coupling and a tiny spontaneous net magnetization further break $T$ symmetry, resulting in a giant anomalous Hall effect (AHE, $\sigma_{xy}>600\,$S/cm, 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 AHE.