Robust midgap states in band-inverted junctions under electric and magnetic fields.

Several IV-VI semiconductor compounds made of heavy atoms, such as Pb Sn Te, may undergo band-inversion at the point of the Brillouin zone upon variation of their chemical composition. This inversion gives rise to topologically distinct phases, characterized by a change in a topological invariant. In the framework of the · theory, band-inversion can be viewed as a change of sign of the fundamental gap.