Microwave Impedance Microscopy of WTe₂

WTe₂ is a van der Waals layered material that behaves as a 2D topological insulator when exfoliated down to a monolayer, supporting edge modes that should be topologically protected. Microwave impedance microscopy (MIM) is a technique that allows real-space mapping of conductivity with a resolution of < 50 nm, and is thus a powerful tool for studying these edge modes that reveals many features that are not accessible to transport measurements alone. Using MIM we observe that the edge is gapless and the edge conduction path conforms to microscopic corners and cracks in the edge and features internal to the monolayer flake. This is consistent with their topological nature and has important consequences for interpreting transport measurements and for making devices employing the 1D helical modes.We also study the behavior of multilayer WTe₂, twisted bilayer WTe₂, and monolayer WTe₂ combined with other materials, such as different capping layers and 2D ferromagnets.