Current propagation behaviors and spin filtering effects in three-terminal topological-insulator junctions

Understand the spin and current behavior in the topological-insulator (TI) system is crucial for the design of electronic and spintronic devices. To study these behaviors, some three-terminal hetero-junction TI systems made from the zigzag silicene-like nanoribbons (ZSiNRs) are investigated. Different external fields are applied in the leads and conductor regions, which result in the expected topological edge states. By calculating the local current distribution, we find two important characteristics of topological edge current propagating in these systems. Firstly, the topological edge current prefers to flow into the nearest channel, rather than the other faraway channels. Secondly, the group-velocity mismatch as a scattering engineering has a significant effect on current propagation behavior. In other words, one can manipulate the topological edge current by velocity mismatch. Based on these characteristics, a type of three-terminal spin filter is proposed in this paper. Moreover, some interesting transport phenomena such as space-separated Fano-resonance are also discovered in the TI-junction systems.