Topological insulators (TI) belong to the phase category which goes beyond the theory of spontaneous symmetry breaking, well describing the classical phases. TI were initially theoretically predicted for materials with strong spin-orbit interactions that lead to the reversal of the sequence of the valence band and the conduction band. Consequently, these materials behave as insulators in the volume while their surfaces host metallic states. The metallic states have an unusual spin structure, with the electron spin locked to its momentum, described by the Dirac-type...
