Description
Altermagnetism is an unconventional magnetic phase characterized by spin-split electronic bands. Using a minimal sublattice-based model, I describe the key symmetry features of this spin splitting [1] and give insights of why and how anomalous Hall effect is expected despite a small total moment [2]. Since many altermagnetic materials are metallic, they can become superconducting either from the magnetic state or from a paramagnetic state. We investigated both possibilities.
In the magnetic state, broken time-reversal symmetry produces spin-split Fermi surfaces, raising the question of how altermagnetic order shapes superconductivity. We find that the sublattice structure strongly influences the superconducting gap, imposing nodal features at Brillouin zone edges for short-range pairing interactions. Extended-range interactions, by contrast, allow pairing at zone edges and can stabilize both spin-singlet and triplet states, with the triplet states exhibiting distinctive nonunitary behavior tied to the altermagnetic order [3].
When superconductivity instead emerges from the paramagnetic state, sublattice polarization suppresses pairing between states on different sublattices and can favor triplet superconductivity driven by next-nearest-neighbor ferromagnetic interactions that are present in some materials.
[1] Mercè Roig, et al., Phys. Rev. B 110, 144412 (2024)
[2] Mercè Roig, et al., Phys. Rev. Lett. 135, 016703 (2025)
[3] Christian L. H. Rasmussen, et al., Phys. Rev. B 113, 174513 (2026)
