Building topologic device through emerging robust helical surface states

In a 3D $Cd_3As_2$ ribbon with proper sizes, the system can exhibit a unique finite-size effect. Namely, if magnetic impurities are doped on one side, the surface states on the other side can be altered according to the strengths of these magnetic impurities. As a result, the conductance of the system will also be changed. This finding can be explained by the backscattering between the hybridized surface states due to finite size confinement and the normal surface states. Moreover, this phenomenon can be used to build new topologic devices.