A gate-tunable quantum phase transition in a topological excitonic insulator

Abstract

Coulomb interactions among electrons and holes in two-dimensional (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, we show 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.

8 pages, 4 figures, under submission

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• Platforms for the realization and characterization of Tomonaga-Luttinger liquids
• Reversal of charge transfer doping on the negative electronic compressibility surface of MoS2
• Excitonic and magnetic phases in doped WTe${}_2$ monolayers: a Hartree-Fock approach
• Engineering excitonic metal-insulator transitions in ultra-thin doped copper sulfides