  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.
