Topological transition from nodal to nodeless Zeeman splitting in altermagnets

Altermagnets are an unconventional type of magnetic state with various appealing properties, both from the fundamental and applied physics perspectives. By investigating the impact of spin-orbit coupling on these states, this work reveals that all altermagnets are intrinsically noncollinear and that their Zeeman splittings possess symmetry-protected nodal lines. These features endow altermagnets with a remarkable resilience against external magnetic fields.