Building topological devices through emerging robust helical surface states

We propose a nonlocal manipulation method to build topological devices through emerging robust helical surface states in Z₂ = 0 topological systems. Specifically, in a ribbon of Z₂ = 0 Bernevig-Hughes-Zhang (BHZ) model with finite-size effect, if magnetic impurities are doped on the top (bottom) edge, the edge states on the bottom (top) edge can be altered according to the strengths and directions of these magnetic impurities. Consequently, the backscattering between the emerging robust helical edge states and gapped normal edge states due to finite-size confinement is also changed, which makes the system alternate between a good one-channel conductor and a good insulator. This effect allows for fabricating topological devices with a high on-off ratio. Furthermore, this proposal can be generalized to three-dimensional (3D) models and more realistic Cd₃As₂ type Dirac semimetals. (paper)