Engineering chiral edge states in 2D topological insulator/ferromagnetic insulator heterostructures

Chiral edge state (CES) at zero magnetic field has already been realized in the magnetically doped topological insulator (TI). However, this scheme strongly relies on material breakthroughs, and in fact, most of the TIs cannot be driven into a Chern insulator in this way. Here, we propose to achieve the CESs in 2D TI/ferromagnetic insulator/TI sandwiched structures through spin-selective coupling between the helical edge states of the two TIs. Due to this coupling, the edge states of one spin channel are gapped and those of the other spin channel remain almost gapless, so that the helical edge states of each isolated TI are changed into the CESs. Such CESs can be hopefully achieved in all TI materials, which are immune to magnetic-disorder-induced backscattering. We propose to implement our scheme in the van der Waals heterostructures between monolayer 1T'-WTe$_2$ and bilayer CrI$_3$. The electrical control of magnetism in bilayer CrI$_3$ switches the transport direction of the CESs, which can realize a low-consumption transistor.