Physicists image topology flip in twisted WSe₂ crystal

A team at Beijing Normal University directly imaged how the Chern number sign in twisted bilayer WSe₂ reverses at a critical twist angle near 1.42°. The result lets engineers set the direction of the Hall current by geometry alone during device fabrication.

• Chern number sign flips at a critical twist angle near 1.42°
• Experiment confirms a 2024 Nature Communications theory prediction
• Measurements spanned twist angles from 1.19° to 1.48° in one device
• Hall current direction is now set by geometry, not trial and error