A Gate‐Tunable Ambipolar Quantum Phase Transition in a Topological Excitonic Insulator

Abstract

Coulomb interactions among electrons and holes in 2D semimetals with overlapping valence and conduction bands can give rise to a correlated insulating ground state via exciton formation and condensation. One candidate material in which such excitonic state uniquely combines with non‐trivial band topology are atomic monolayers of tungsten ditelluride (WTe2), in which a 2D topological excitonic insulator (2D TEI) forms. However, the detailed mechanism of the 2D bulk gap formation in WTe2, in particular with regard to the role of Coulomb interactions, has remained a subject of ongoing debate. Here, it shows that WTe2 is susceptible to a gate‐tunable quantum phase transition, evident from an abrupt collapse of its 2D bulk energy gap upon ambipolar field‐effect doping. Such gate tunability of a 2D TEI, into either n‐ and p‐type semimetals, promises novel handles of control over non‐trivial 2D superconductivity with excitonic pairing.