Helical antiferromagnets: Revealing band spin texture of momentum-odd symmetry

In low-symmetry antiferromagnets (AFMs), electronic bands can exhibit momentum-dependent spin splitting even in the absence of spin-orbit coupling (SOC). In the context of spintronics applications, AFMs displaying momentum-odd band spin textures [S(–k) = –S(k)] may be particularly attractive, as the energy scale of spin splitting is significantly enhanced by exchange interactions compared to non-magnetic Rashba SOC systems.

In this presentation, we demonstrate that such spin textures commonly occur in helical spin-spiral magnets with a cone angle of 90 degrees. In these flat spiral states, the net magnetization is zero; however, each individual band can possess a spin S(k) that is polarized normal to the spiral plane and exhibits odd symmetry with respect to momentum k. This phenomenon is illustrated using a simple one-band model and density-functional theory calculations. Furthermore, we will show that the irreducible representation of S(k) can be readily obtained through a straightforward symmetry analysis within the framework of the generalized Bloch theorem.