Recent studies have demonstrated that topological quantum spin Hall (QSH) states exist in twisted bilayers of transition metal dichalcogenides. However, a comprehensive theoretical characterization of the topological edge states remains a topic of interest and an unresolved issue. Here, the topological transport properties of the twisted ${\mathrm{WSe}}_2$ bilayers are investigated. Beyond the conventional single QSH state, we identify emergent double and fourfold QSH states, hosting two and four pairs of counter-propagating helical edge channels respectively. Furthermore, the charge carriers in these edge states are not localized at the geometric edge but rather the potential maxima of the moiré superlattice boundary, undergoing interlayer transitions and propagating forward continuously. We term these edge states as moiré edge states. These edge states can survive in non-magnetic disorder, with the robustness of double QSH states surpassing that of single QSH states. At a twisting angle of $2.{45}^{\circ }$, the transition between the single and double QSH states can be achieved by adjusting the gate on the surface. Based on this, we propose a five-terminal device as a topological current divider. Our findings provide support for the development of dissipationless spintronics.

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• Topological insulators
• Dichalcogenides
• Nanoribbon
• Two-dimensional electron system
• Green's function methods