Rodrigo G. Pereira
Altermagnets are distinguished by a magnetic order parameter that exhibits a nontrivial angular dependence both in real and momentum space, and a resulting momentum-dependent spin-splitting that is present even in absence of spin-orbit coupling. In this talk I will discuss the impact of the crystalline environment, enabled by the spin-orbit coupling, on the magnetic and electronic properties of an altermagnet. We find that, because each component of the magnetization acquires its own angular dependence, the Zeeman splitting of the bands has symmetry-protected nodal lines residing on mirror planes of the crystal. We show that an external magnetic field perpendicular to these mirror planes can only move the nodal lines, such that a critical field value is necessary to collapse the nodes and make the Weyl pinch points annihilate. This unveils the topological nature of the transition from a nodal to a nodeless Zeeman splitting of the bands.