Light-Induced Even-Parity Unidirectional Spin Splitting in Coplanar Antiferromagnets

TL;DR

This paper proposes a method to induce even-parity, out-of-plane spin splitting in coplanar antiferromagnets using circularly polarized light, creating a new class of optically controllable spin-split phases with unique momentum-space textures.

Contribution

It introduces a symmetry-based approach to generate even-parity spin splitting in coplanar AFMs via optical driving, expanding the possibilities for spintronic materials.

Findings

Light irradiation lifts symmetry constraints, enabling even-parity spin splitting.

The induced spin splitting exhibits a robust d-wave momentum-space texture.

The resulting spin conductivity has a distinctive clover-like angular dependence.

Abstract

When a coplanar antiferromagnet (AFM) with $xy$-plane magnetic moments exhibits a spin-split band structure and unidirectional spin polarization along $z$, the spin polarization is forced to be an odd function of momentum by the fundamental symmetry $[\bar{C}_{2z}\|\mathcal{T}]$. Coplanar AFMs displaying such odd-parity unidirectional spin splittings are known as odd-parity magnets. In this work, we propose the realization of their missing even-parity counterparts. We begin by deriving the symmetry conditions required for an even-parity, out-of-plane spin splitting. We then show that irradiating a spin-degenerate coplanar AFM with circularly polarized light lifts the $[\bar{C}_{2z}|\mathcal{T}]$ constraint, dynamically generating this even-parity state. Specifically, the light-induced unidirectional spin splitting exhibits a $d$-wave texture in momentum space, akin to that of a $d$-wave altermagnet. We prove this texture's robustness against spin canting and show it yields a unique clover-like angular dependence in the Drude spin conductivity. Our work demonstrates that optical driving can generate novel spin-split phases in coplanar AFMs, thereby diversifying the landscape of materials exhibiting distinct spin splittings.