Weyl semimetal in ultra-thin film of topological insulator multilayer
  In ultra-thin film of topological insulator, the hybridization between the top and bottom surfaces opens an energy gap and forms two degenerate quantum anomalous Hall states, which give rise to a quantum spin Hall state. In this paper, we demonstrate that a Weyl semimetal can be realized in an ultra-thin film of topological insulator heterostructure in a similar way to that of the surface state of a strong three-dimensional (3D) topological insulator studied by Burkov and Balents . We find that the system realizes both 3D quantum anomalous Hall phase and 3D quantum spin Hall phase, and the Weyl nodes occur at zero energy when both time-reversal symmetry and inversion symmetry are explicitly broken by the magnetic field and the structure inversion asymmetry of the thin film. 
S. A. Owerre
cond-mat.str-el cond-mat.mes-hall