In recent years, theoretical physicists discovered that the topology of a material can lead to interesting new quantum properties. This simple concept can be applied to the electronic structure of semiconducting materials in which relativistic effects are important. In 2015, several materials like NbP, NbAs, TaP, TaAs, und MoTe2
have been suggested by theoreticians as promissing, so-called Weyl semimetals, and have been physically characterized just a bit later. The special feature is that Weyl fermions, which occur in these materials as quasiparticles, exist in two chiralities.