  The electronic transport properties in magnetically doped ultra-thin films of
topological-insulators is investigated by using Landauer-buttiker formalism.
The chiral selective tunneling is addressed in such systems which leads to
transport gap and as a consequence current blocking. This quantum blocking of
transport occurs when the magnetic states with opposite chirality are aligned
energetically. This can be obsereved when an electron tunnels through a barrier
or well of magnetic potential induced by the exchange field. It is proved and
demonstrated that this chiral transition rule fails when structural inversion
asymmetric potential or an in-plane magnetization is turning on. This new
finding is useful to interpret quantum transport through topological-insulator
thin films especially to shed light on longitudinal conductance behavior of
quantum anomalous Hall effect. Besides, one can design electronic devices by
means of magnetic topological-insulator thin films based on the chiral
selective tunneling leading to negative differential resistance.
