From Weyl semimetal to Quantum anomalous Hall effect and Majorana Fermi

    Weyl semimetals (WSMs) are a recently discovered topological quantum state that can be observed in condensed matter physics. In WSMs, the conduction band and valence band linearly touch each other at the Weyl nodes, the sinks and sources of Berry curvature. A Weyl semimetal can exist in a time-reversal or inversion-symmetry breaking system. Since the Berry curvature is odd under time reversal, the Berry curvature from Weyl points are expected to generate a large anomalous Hall effect (AHE) in time reversal symmetry breaking WSMs [1].

    The magnetic WSMs can be viewed as the three-dimensional quantum anomalous Hall effect, and the its quantum confinement is expected to lead to quantum anomalous Hall insulator (QAHI) in two-dimension limitation. This can be understood from the simplest minimal two band model with two Weyl points locating at ±kz, where the open boundary condition can give a QAHI, see Fig. 1. Integral of QAHI in the heterostructure together with topological insulator can generate the chiral Majorana edge states. Compared to Majorana bound state, the Majorana edge states can be directly observed by transport and offers an excellent candidate for the quantum computing.

    Fig. 1 Evolution from WSM to QAHI Zoom Image
    Fig. 1 Evolution from WSM to QAHI

    Our group has extensive experiences in the studying of topological semimetals and magnetic materials. Very recently, a large class of magnetic WSMs were proposed in Heusler compounds and layered materials [2], which provides good candidate for realization of intrinsic QAHI by quantum confidents. In comparison with QAHI from magnetic doped topological insulators, intrinsic QAHI can have high Curie temperature and large band gap, which are the strong advantages for the application of QAHI itself and in the generation of Majorana Fermions.

    [1] Wan, X. G. et al., Phys. Rev. B 83, 205101 (2011).
    [2] Wang, Z. et al.  Phy. Rev. Lett. 117, 236401 (2016);
         Chang, G. et al.  Sci. Rep. 6, 38839 (2016).

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