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

TL;DR

This paper demonstrates that monolayer WTe2 can undergo a gate-tunable quantum phase transition, collapsing its 2D bulk gap and enabling control over topological excitonic insulator states and potential superconductivity.

Contribution

It reveals the gate-tunable quantum phase transition in WTe2, advancing understanding of Coulomb interactions and topological excitonic insulators in 2D materials.

Findings

Abrupt collapse of 2D bulk energy gap with doping

Gate control over topological excitonic insulator state

Potential for inducing 2D superconductivity

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.