The observation of quantized Chern numbers in twisted transition metal dichalcogenide homobilayers, including 3.7° twisted ${\mathrm{MoTe}}_2$ and 1.23° twisted ${\mathrm{WSe}}_2$, represents a landmark breakthrough in moiré physics. A striking and unresolved paradox to emerge from these studies is the unexpected opposite sign of the measured Chern numbers between the two systems, a discrepancy that strongly hints at a twist-angle-dependent reversal of the Chern number sign. Despite this compelling implication, direct experimental validation of such a sign reversal within a single twisted transition metal dichalcogenide homobilayer system is still elusive. Here, we report the first experimental demonstration that the Chern numbers of the moiré frontier bands undergo sign reversal at a critical twist angle $\sim 1.42°$ in twisted ${\mathrm{WSe}}_2$ bilayers (${\mathrm{tWSe}}_2$). Using scanning tunneling microscopy and spectroscopy, we directly measure layer-pseudospin skyrmion textures of ${\mathrm{tWSe}}_2$ and our results reveal that ${\mathrm{tWSe}}_2$ in the vicinity of the 1.42° exhibits a twist-angle-dependent layer-pseudospin polarization, an effect that serves as the fundamental origin of the observed Chern number sign reversal.

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• Flat bands
• 2-dimensional systems
• Moire materials
• Transition metal dichalcogenides
• Scanning tunneling microscopy