Time-Reversal Symmetry Breaking Type-II Weyl State in YbMnBi2

Understand

Detection of Dirac, Majorana and Weyl fermions in real materials may significantly strengthen the bridge between high-energy and condensed-matter physics.

• While the presence of Dirac fermions is well established in graphene and topological insulators, Majorana particles have been reported recently and evidence for Weyl fermions in non-centrosymmetric crystals has been found only a couple of months ago, the 'magnetic' Weyl fermions are still elusive despite numerous theoretical predictions and intense experimental search.
• In order to detect a time-reversal symmetry breaking Weyl state we designed two materials with Fermi velocities superior to that of graphene and present here the experimental evidence of the realization of such a state in one of them, YbMnBi2.
• We model the time reversal symmetry breaking observed by magnetization measurements by a canted antiferromagnetic state and find a number of Weyl points both above and below the Fermi level.