Ideal Weyl semimetal induced by magnetic exchange

Weyl semimetals exhibit anomalous electronic transport due to the presence of topological band crossings, called Weyl nodes. In this work, experimental and theoretical results show that EuCd${}_{2}$As${}_{2}$ in a magnetic field is what Bernevig has termed the hydrogen atom of a Weyl semimetal, i.e. one with a single pair of Weyl nodes at the Fermi level and without overlapping electron bands. The discovery opens the door to a wide range of exotic physics, predicted for Weyl fermions in the solid state.