Wang, Z., Garcia Vergniory, M., Kushawa, S., Hirschberger, M., Chulkov, E. V., Ernst, A., Ong, N. P., Cava, R. J., Bernevig, B. A.

Time-reversal-breaking Weyl fermions in magnetic Heusler alloys
Physical Review Letters **117**, (23),pp 236401/1-6 (2016)
Weyl fermions have recently beenobserved in several time-reversal-invariant semimetals and photonics materials with broken inversion symmetry. These systems are expected to have exotic transport properties such as the chiral anomaly. However, most discovered Weyl materials possess a substantial number of Weyl nodes close to the Fermi level that give rise to complicated transport properties. Here we predict, for the first time, a new family of Weyl systems defined by broken time-reversal symmetry, namely Co-based magnetic Heusler materials (XCo_{2}Z (X=IVB; Z= IVA or IIIA). To search for Weyl fermions in the centrosymmetric magnetic systems, we recall an easy and practical invariant, which has been calculated to be -1, guaranteeing the existence of an odd number of pairs of Weyl fermions. These materials exhibit, when alloyed, only two Weyl nodes at the Fermi level - the minimum number possible in a condensed matter system. The Weyl nodes are protected by the rotational symmetry alon gthe magnetic axis and separated by a lkarge distance (of order 2π) in the Brillouin zone. The corresponding Fermi arcs have been calculated as well. The discovery provides a realistic and promising platform formanipulating and studying the magnetic Weyl physics in experiments.

TH-2016-46