Chern number of thin films of the topological insulator Bi2Se3

In thin films of Bi2Se3, the isospin sectors have nontrivial topological properties, which are conventionally characterized by the Z(2) index. The generalized isospin Chern number [E. Prodan, Phys. Rev. B 80, 125327 (2009)] is calculated in the general case where the structural inversion symmetry is broken and the isospin operator (tau) over cap (z) is not conserved. The analytical formalism obtained reveals clearly the connection between the isospin Chern number and the Z2 index. We further demonstrate that the topological characterization based on the isospin Chern number fully agrees with the characteristic spectrum of the edge states in different regimes.