Properties of the insulating, metallic and superconducting states in monolayer WTe₂

When the layered semimetal WTe₂ is thinned down to a monolayer, it becomes a topological insulator that turns metallic or superconducting under moderate electrostatic doping. The insulator is not only topological but is also posited to be an excitonic insulator; meanwhile, the induced superconductor is very dilute and sensitive to disorder. We implemented a new growth technique that greatly improves the quality of WTe₂ crystals, producing a record residual resistivity ratio and magnetoresistance. Monolayers now exhibit quantum oscillations that reflect the Fermi surface in the metallic states and an electron-doped superconducting dome with Tc reaching 1.8 K. The insulator still shows signs of excitonic pairing, and I will propose two possible explanations for the absence of symmetry breaking, a feature that sets it apart from other excitonic insulator candidates. I will also discuss the effects of combining monolayer WTe₂ with graphene to create a hybrid 2D semimetal.