Prediction of new prototypes of non-relativistic spin splitting in antiferromagnets-beyond altermagnets

The breaking of both space-time-reversal and translational-spin-reversal symmetries enables splitting between spin energy bands in antiferromagnets even without the traditional spin-orbit coupling [‘non-relativistic spin splitting’ (NRSS)], as exemplified by MnF₂. Here, it is pointed out that depending on additional auxiliary symmetries of spin interconversion, NRSS antiferromagnets break into subgroups having notably different patterns of spin splitting and spin textures. The recently coined ‘altermagnetism’ (e.g., MnF₂) is one of these subgroups. Using the above auxiliary symmetries as filters for sorting out real compounds, we identify materials belonging to the different subgroups, including spin splitting at the Brillouin zone center (a-type), and different forms of spin polarization (g-type). Predictions are validated by Density Functional calculations, creating a basis for future experimental testing. The magnitude of the spin splitting of some of the discovered prototypes surpasses the Rashba and Dresselhaus spin splitting in semiconductors and the ‘altermagnetism’ subgroup (b-type) with their spin splitting away from the Brillouin zone center. Furthermore, we find large spin splitting with Zeeman-type spin texture at the zone center in a NRSS prototype. This offers a rich platform for designing new spintronic materials.